parse_relation.c

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/*-------------------------------------------------------------------------
 *
 * parse_relation.c
 *    parser support routines dealing with relations
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/parser/parse_relation.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>

#include "access/htup_details.h"
#include "access/relation.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "catalog/heap.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_enr.h"
#include "parser/parse_relation.h"
#include "parser/parse_type.h"
#include "parser/parsetree.h"
#include "storage/lmgr.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/varlena.h"


/*
 * Support for fuzzily matching columns.
 *
 * This is for building diagnostic messages, where non-exact matching
 * attributes are suggested to the user.  The struct's fields may be facets of
 * a particular RTE, or of an entire range table, depending on context.
 */
typedef struct
{
    int         distance;       /* Weighted distance (lowest so far) */
    RangeTblEntry *rfirst;      /* RTE of first */
    AttrNumber  first;          /* Closest attribute so far */
    RangeTblEntry *rsecond;     /* RTE of second */
    AttrNumber  second;         /* Second closest attribute so far */
} FuzzyAttrMatchState;

#define MAX_FUZZY_DISTANCE              3


static ParseNamespaceItem *scanNameSpaceForRefname(ParseState *pstate,
                                                   const char *refname,
                                                   int location);
static ParseNamespaceItem *scanNameSpaceForRelid(ParseState *pstate, Oid relid,
                                                 int location);
static void check_lateral_ref_ok(ParseState *pstate, ParseNamespaceItem *nsitem,
                                 int location);
static int  scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte,
                             const char *colname, int location,
                             int fuzzy_rte_penalty,
                             FuzzyAttrMatchState *fuzzystate);
static void markRTEForSelectPriv(ParseState *pstate, RangeTblEntry *rte,
                                 int rtindex, AttrNumber col);
static void expandRelation(Oid relid, Alias *eref,
                           int rtindex, int sublevels_up,
                           int location, bool include_dropped,
                           List **colnames, List **colvars);
static void expandTupleDesc(TupleDesc tupdesc, Alias *eref,
                            int count, int offset,
                            int rtindex, int sublevels_up,
                            int location, bool include_dropped,
                            List **colnames, List **colvars);
static int  specialAttNum(const char *attname);
static bool isQueryUsingTempRelation_walker(Node *node, void *context);


/*
 * refnameNamespaceItem
 *    Given a possibly-qualified refname, look to see if it matches any visible
 *    namespace item.  If so, return a pointer to the nsitem; else return NULL.
 *
 *    Optionally get nsitem's nesting depth (0 = current) into *sublevels_up.
 *    If sublevels_up is NULL, only consider items at the current nesting
 *    level.
 *
 * An unqualified refname (schemaname == NULL) can match any item with matching
 * alias, or matching unqualified relname in the case of alias-less relation
 * items.  It is possible that such a refname matches multiple items in the
 * nearest nesting level that has a match; if so, we report an error via
 * ereport().
 *
 * A qualified refname (schemaname != NULL) can only match a relation item
 * that (a) has no alias and (b) is for the same relation identified by
 * schemaname.refname.  In this case we convert schemaname.refname to a
 * relation OID and search by relid, rather than by alias name.  This is
 * peculiar, but it's what SQL says to do.
 */
ParseNamespaceItem *
refnameNamespaceItem(ParseState *pstate,
                     const char *schemaname,
                     const char *refname,
                     int location,
                     int *sublevels_up)
{
    Oid         relId = InvalidOid;

    if (sublevels_up)
        *sublevels_up = 0;

    if (schemaname != NULL)
    {
        Oid         namespaceId;

        /*
         * We can use LookupNamespaceNoError() here because we are only
         * interested in finding existing RTEs.  Checking USAGE permission on
         * the schema is unnecessary since it would have already been checked
         * when the RTE was made.  Furthermore, we want to report "RTE not
         * found", not "no permissions for schema", if the name happens to
         * match a schema name the user hasn't got access to.
         */
        namespaceId = LookupNamespaceNoError(schemaname);
        if (!OidIsValid(namespaceId))
            return NULL;
        relId = get_relname_relid(refname, namespaceId);
        if (!OidIsValid(relId))
            return NULL;
    }

    while (pstate != NULL)
    {
        ParseNamespaceItem *result;

        if (OidIsValid(relId))
            result = scanNameSpaceForRelid(pstate, relId, location);
        else
            result = scanNameSpaceForRefname(pstate, refname, location);

        if (result)
            return result;

        if (sublevels_up)
            (*sublevels_up)++;
        else
            break;

        pstate = pstate->parentParseState;
    }
    return NULL;
}

/*
 * Search the query's table namespace for an item matching the
 * given unqualified refname.  Return the nsitem if a unique match, or NULL
 * if no match.  Raise error if multiple matches.
 *
 * Note: it might seem that we shouldn't have to worry about the possibility
 * of multiple matches; after all, the SQL standard disallows duplicate table
 * aliases within a given SELECT level.  Historically, however, Postgres has
 * been laxer than that.  For example, we allow
 *      SELECT ... FROM tab1 x CROSS JOIN (tab2 x CROSS JOIN tab3 y) z
 * on the grounds that the aliased join (z) hides the aliases within it,
 * therefore there is no conflict between the two RTEs named "x".  However,
 * if tab3 is a LATERAL subquery, then from within the subquery both "x"es
 * are visible.  Rather than rejecting queries that used to work, we allow
 * this situation, and complain only if there's actually an ambiguous
 * reference to "x".
 */
static ParseNamespaceItem *
scanNameSpaceForRefname(ParseState *pstate, const char *refname, int location)
{
    ParseNamespaceItem *result = NULL;
    ListCell   *l;

    foreach(l, pstate->p_namespace)
    {
        ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(l);
        RangeTblEntry *rte = nsitem->p_rte;

        /* Ignore columns-only items */
        if (!nsitem->p_rel_visible)
            continue;
        /* If not inside LATERAL, ignore lateral-only items */
        if (nsitem->p_lateral_only && !pstate->p_lateral_active)
            continue;

        if (strcmp(rte->eref->aliasname, refname) == 0)
        {
            if (result)
                ereport(ERROR,
                        (errcode(ERRCODE_AMBIGUOUS_ALIAS),
                         errmsg("table reference \"%s\" is ambiguous",
                                refname),
                         parser_errposition(pstate, location)));
            check_lateral_ref_ok(pstate, nsitem, location);
            result = nsitem;
        }
    }
    return result;
}

/*
 * Search the query's table namespace for a relation item matching the
 * given relation OID.  Return the nsitem if a unique match, or NULL
 * if no match.  Raise error if multiple matches.
 *
 * See the comments for refnameNamespaceItem to understand why this
 * acts the way it does.
 */
static ParseNamespaceItem *
scanNameSpaceForRelid(ParseState *pstate, Oid relid, int location)
{
    ParseNamespaceItem *result = NULL;
    ListCell   *l;

    foreach(l, pstate->p_namespace)
    {
        ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(l);
        RangeTblEntry *rte = nsitem->p_rte;

        /* Ignore columns-only items */
        if (!nsitem->p_rel_visible)
            continue;
        /* If not inside LATERAL, ignore lateral-only items */
        if (nsitem->p_lateral_only && !pstate->p_lateral_active)
            continue;

        /* yes, the test for alias == NULL should be there... */
        if (rte->rtekind == RTE_RELATION &&
            rte->relid == relid &&
            rte->alias == NULL)
        {
            if (result)
                ereport(ERROR,
                        (errcode(ERRCODE_AMBIGUOUS_ALIAS),
                         errmsg("table reference %u is ambiguous",
                                relid),
                         parser_errposition(pstate, location)));
            check_lateral_ref_ok(pstate, nsitem, location);
            result = nsitem;
        }
    }
    return result;
}

/*
 * Search the query's CTE namespace for a CTE matching the given unqualified
 * refname.  Return the CTE (and its levelsup count) if a match, or NULL
 * if no match.  We need not worry about multiple matches, since parse_cte.c
 * rejects WITH lists containing duplicate CTE names.
 */
CommonTableExpr *
scanNameSpaceForCTE(ParseState *pstate, const char *refname,
                    Index *ctelevelsup)
{
    Index       levelsup;

    for (levelsup = 0;
         pstate != NULL;
         pstate = pstate->parentParseState, levelsup++)
    {
        ListCell   *lc;

        foreach(lc, pstate->p_ctenamespace)
        {
            CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

            if (strcmp(cte->ctename, refname) == 0)
            {
                *ctelevelsup = levelsup;
                return cte;
            }
        }
    }
    return NULL;
}

/*
 * Search for a possible "future CTE", that is one that is not yet in scope
 * according to the WITH scoping rules.  This has nothing to do with valid
 * SQL semantics, but it's important for error reporting purposes.
 */
static bool
isFutureCTE(ParseState *pstate, const char *refname)
{
    for (; pstate != NULL; pstate = pstate->parentParseState)
    {
        ListCell   *lc;

        foreach(lc, pstate->p_future_ctes)
        {
            CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

            if (strcmp(cte->ctename, refname) == 0)
                return true;
        }
    }
    return false;
}

/*
 * Search the query's ephemeral named relation namespace for a relation
 * matching the given unqualified refname.
 */
bool
scanNameSpaceForENR(ParseState *pstate, const char *refname)
{
    return name_matches_visible_ENR(pstate, refname);
}

/*
 * searchRangeTableForRel
 *    See if any RangeTblEntry could possibly match the RangeVar.
 *    If so, return a pointer to the RangeTblEntry; else return NULL.
 *
 * This is different from refnameNamespaceItem in that it considers every
 * entry in the ParseState's rangetable(s), not only those that are currently
 * visible in the p_namespace list(s).  This behavior is invalid per the SQL
 * spec, and it may give ambiguous results (there might be multiple equally
 * valid matches, but only one will be returned).  This must be used ONLY
 * as a heuristic in giving suitable error messages.  See errorMissingRTE.
 *
 * Notice that we consider both matches on actual relation (or CTE) name
 * and matches on alias.
 */
static RangeTblEntry *
searchRangeTableForRel(ParseState *pstate, RangeVar *relation)
{
    const char *refname = relation->relname;
    Oid         relId = InvalidOid;
    CommonTableExpr *cte = NULL;
    bool        isenr = false;
    Index       ctelevelsup = 0;
    Index       levelsup;

    /*
     * If it's an unqualified name, check for possible CTE matches. A CTE
     * hides any real relation matches.  If no CTE, look for a matching
     * relation.
     *
     * NB: It's not critical that RangeVarGetRelid return the correct answer
     * here in the face of concurrent DDL.  If it doesn't, the worst case
     * scenario is a less-clear error message.  Also, the tables involved in
     * the query are already locked, which reduces the number of cases in
     * which surprising behavior can occur.  So we do the name lookup
     * unlocked.
     */
    if (!relation->schemaname)
    {
        cte = scanNameSpaceForCTE(pstate, refname, &ctelevelsup);
        if (!cte)
            isenr = scanNameSpaceForENR(pstate, refname);
    }

    if (!cte && !isenr)
        relId = RangeVarGetRelid(relation, NoLock, true);

    /* Now look for RTEs matching either the relation/CTE/ENR or the alias */
    for (levelsup = 0;
         pstate != NULL;
         pstate = pstate->parentParseState, levelsup++)
    {
        ListCell   *l;

        foreach(l, pstate->p_rtable)
        {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

            if (rte->rtekind == RTE_RELATION &&
                OidIsValid(relId) &&
                rte->relid == relId)
                return rte;
            if (rte->rtekind == RTE_CTE &&
                cte != NULL &&
                rte->ctelevelsup + levelsup == ctelevelsup &&
                strcmp(rte->ctename, refname) == 0)
                return rte;
            if (rte->rtekind == RTE_NAMEDTUPLESTORE &&
                isenr &&
                strcmp(rte->enrname, refname) == 0)
                return rte;
            if (strcmp(rte->eref->aliasname, refname) == 0)
                return rte;
        }
    }
    return NULL;
}

/*
 * Check for relation-name conflicts between two namespace lists.
 * Raise an error if any is found.
 *
 * Note: we assume that each given argument does not contain conflicts
 * itself; we just want to know if the two can be merged together.
 *
 * Per SQL, two alias-less plain relation RTEs do not conflict even if
 * they have the same eref->aliasname (ie, same relation name), if they
 * are for different relation OIDs (implying they are in different schemas).
 *
 * We ignore the lateral-only flags in the namespace items: the lists must
 * not conflict, even when all items are considered visible.  However,
 * columns-only items should be ignored.
 */
void
checkNameSpaceConflicts(ParseState *pstate, List *namespace1,
                        List *namespace2)
{
    ListCell   *l1;

    foreach(l1, namespace1)
    {
        ParseNamespaceItem *nsitem1 = (ParseNamespaceItem *) lfirst(l1);
        RangeTblEntry *rte1 = nsitem1->p_rte;
        const char *aliasname1 = rte1->eref->aliasname;
        ListCell   *l2;

        if (!nsitem1->p_rel_visible)
            continue;

        foreach(l2, namespace2)
        {
            ParseNamespaceItem *nsitem2 = (ParseNamespaceItem *) lfirst(l2);
            RangeTblEntry *rte2 = nsitem2->p_rte;

            if (!nsitem2->p_rel_visible)
                continue;
            if (strcmp(rte2->eref->aliasname, aliasname1) != 0)
                continue;       /* definitely no conflict */
            if (rte1->rtekind == RTE_RELATION && rte1->alias == NULL &&
                rte2->rtekind == RTE_RELATION && rte2->alias == NULL &&
                rte1->relid != rte2->relid)
                continue;       /* no conflict per SQL rule */
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_ALIAS),
                     errmsg("table name \"%s\" specified more than once",
                            aliasname1)));
        }
    }
}

/*
 * Complain if a namespace item is currently disallowed as a LATERAL reference.
 * This enforces both SQL:2008's rather odd idea of what to do with a LATERAL
 * reference to the wrong side of an outer join, and our own prohibition on
 * referencing the target table of an UPDATE or DELETE as a lateral reference
 * in a FROM/USING clause.
 *
 * Note: the pstate should be the same query level the nsitem was found in.
 *
 * Convenience subroutine to avoid multiple copies of a rather ugly ereport.
 */
static void
check_lateral_ref_ok(ParseState *pstate, ParseNamespaceItem *nsitem,
                     int location)
{
    if (nsitem->p_lateral_only && !nsitem->p_lateral_ok)
    {
        /* SQL:2008 demands this be an error, not an invisible item */
        RangeTblEntry *rte = nsitem->p_rte;
        char       *refname = rte->eref->aliasname;

        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("invalid reference to FROM-clause entry for table \"%s\"",
                        refname),
                 (pstate->p_target_nsitem != NULL &&
                  rte == pstate->p_target_nsitem->p_rte) ?
                 errhint("There is an entry for table \"%s\", but it cannot be referenced from this part of the query.",
                         refname) :
                 errdetail("The combining JOIN type must be INNER or LEFT for a LATERAL reference."),
                 parser_errposition(pstate, location)));
    }
}

/*
 * Given an RT index and nesting depth, find the corresponding
 * ParseNamespaceItem (there must be one).
 */
ParseNamespaceItem *
GetNSItemByRangeTablePosn(ParseState *pstate,
                          int varno,
                          int sublevels_up)
{
    ListCell   *lc;

    while (sublevels_up-- > 0)
    {
        pstate = pstate->parentParseState;
        Assert(pstate != NULL);
    }
    foreach(lc, pstate->p_namespace)
    {
        ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(lc);

        if (nsitem->p_rtindex == varno)
            return nsitem;
    }
    elog(ERROR, "nsitem not found (internal error)");
    return NULL;                /* keep compiler quiet */
}

/*
 * Given an RT index and nesting depth, find the corresponding RTE.
 * (Note that the RTE need not be in the query's namespace.)
 */
RangeTblEntry *
GetRTEByRangeTablePosn(ParseState *pstate,
                       int varno,
                       int sublevels_up)
{
    while (sublevels_up-- > 0)
    {
        pstate = pstate->parentParseState;
        Assert(pstate != NULL);
    }
    Assert(varno > 0 && varno <= list_length(pstate->p_rtable));
    return rt_fetch(varno, pstate->p_rtable);
}

/*
 * Fetch the CTE for a CTE-reference RTE.
 *
 * rtelevelsup is the number of query levels above the given pstate that the
 * RTE came from.
 */
CommonTableExpr *
GetCTEForRTE(ParseState *pstate, RangeTblEntry *rte, int rtelevelsup)
{
    Index       levelsup;
    ListCell   *lc;

    Assert(rte->rtekind == RTE_CTE);
    levelsup = rte->ctelevelsup + rtelevelsup;
    while (levelsup-- > 0)
    {
        pstate = pstate->parentParseState;
        if (!pstate)            /* shouldn't happen */
            elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
    }
    foreach(lc, pstate->p_ctenamespace)
    {
        CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

        if (strcmp(cte->ctename, rte->ctename) == 0)
            return cte;
    }
    /* shouldn't happen */
    elog(ERROR, "could not find CTE \"%s\"", rte->ctename);
    return NULL;                /* keep compiler quiet */
}

/*
 * updateFuzzyAttrMatchState
 *    Using Levenshtein distance, consider if column is best fuzzy match.
 */
static void
updateFuzzyAttrMatchState(int fuzzy_rte_penalty,
                          FuzzyAttrMatchState *fuzzystate, RangeTblEntry *rte,
                          const char *actual, const char *match, int attnum)
{
    int         columndistance;
    int         matchlen;

    /* Bail before computing the Levenshtein distance if there's no hope. */
    if (fuzzy_rte_penalty > fuzzystate->distance)
        return;

    /*
     * Outright reject dropped columns, which can appear here with apparent
     * empty actual names, per remarks within scanRTEForColumn().
     */
    if (actual[0] == '\0')
        return;

    /* Use Levenshtein to compute match distance. */
    matchlen = strlen(match);
    columndistance =
        varstr_levenshtein_less_equal(actual, strlen(actual), match, matchlen,
                                      1, 1, 1,
                                      fuzzystate->distance + 1
                                      - fuzzy_rte_penalty,
                                      true);

    /*
     * If more than half the characters are different, don't treat it as a
     * match, to avoid making ridiculous suggestions.
     */
    if (columndistance > matchlen / 2)
        return;

    /*
     * From this point on, we can ignore the distinction between the RTE-name
     * distance and the column-name distance.
     */
    columndistance += fuzzy_rte_penalty;

    /*
     * If the new distance is less than or equal to that of the best match
     * found so far, update fuzzystate.
     */
    if (columndistance < fuzzystate->distance)
    {
        /* Store new lowest observed distance for RTE */
        fuzzystate->distance = columndistance;
        fuzzystate->rfirst = rte;
        fuzzystate->first = attnum;
        fuzzystate->rsecond = NULL;
        fuzzystate->second = InvalidAttrNumber;
    }
    else if (columndistance == fuzzystate->distance)
    {
        /*
         * This match distance may equal a prior match within this same range
         * table.  When that happens, the prior match may also be given, but
         * only if there is no more than two equally distant matches from the
         * RTE (in turn, our caller will only accept two equally distant
         * matches overall).
         */
        if (AttributeNumberIsValid(fuzzystate->second))
        {
            /* Too many RTE-level matches */
            fuzzystate->rfirst = NULL;
            fuzzystate->first = InvalidAttrNumber;
            fuzzystate->rsecond = NULL;
            fuzzystate->second = InvalidAttrNumber;
            /* Clearly, distance is too low a bar (for *any* RTE) */
            fuzzystate->distance = columndistance - 1;
        }
        else if (AttributeNumberIsValid(fuzzystate->first))
        {
            /* Record as provisional second match for RTE */
            fuzzystate->rsecond = rte;
            fuzzystate->second = attnum;
        }
        else if (fuzzystate->distance <= MAX_FUZZY_DISTANCE)
        {
            /*
             * Record as provisional first match (this can occasionally occur
             * because previous lowest distance was "too low a bar", rather
             * than being associated with a real match)
             */
            fuzzystate->rfirst = rte;
            fuzzystate->first = attnum;
        }
    }
}

/*
 * scanNSItemForColumn
 *    Search the column names of a single namespace item for the given name.
 *    If found, return an appropriate Var node, else return NULL.
 *    If the name proves ambiguous within this nsitem, raise error.
 *
 * Side effect: if we find a match, mark the item's RTE as requiring read
 * access for the column.
 */
Node *
scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
                    int sublevels_up, const char *colname, int location)
{
    RangeTblEntry *rte = nsitem->p_rte;
    int         attnum;
    Var        *var;

    /*
     * Scan the RTE's column names (or aliases) for a match.  Complain if
     * multiple matches.
     */
    attnum = scanRTEForColumn(pstate, rte,
                              colname, location,
                              0, NULL);

    if (attnum == InvalidAttrNumber)
        return NULL;            /* Return NULL if no match */

    /* In constraint check, no system column is allowed except tableOid */
    if (pstate->p_expr_kind == EXPR_KIND_CHECK_CONSTRAINT &&
        attnum < InvalidAttrNumber && attnum != TableOidAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("system column \"%s\" reference in check constraint is invalid",
                        colname),
                 parser_errposition(pstate, location)));

    /* In generated column, no system column is allowed except tableOid */
    if (pstate->p_expr_kind == EXPR_KIND_GENERATED_COLUMN &&
        attnum < InvalidAttrNumber && attnum != TableOidAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("cannot use system column \"%s\" in column generation expression",
                        colname),
                 parser_errposition(pstate, location)));

    /* Found a valid match, so build a Var */
    if (attnum > InvalidAttrNumber)
    {
        /* Get attribute data from the ParseNamespaceColumn array */
        ParseNamespaceColumn *nscol = &nsitem->p_nscolumns[attnum - 1];

        /* Complain if dropped column.  See notes in scanRTEForColumn. */
        if (nscol->p_varno == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_COLUMN),
                     errmsg("column \"%s\" of relation \"%s\" does not exist",
                            colname,
                            rte->eref->aliasname)));

        var = makeVar(nscol->p_varno,
                      nscol->p_varattno,
                      nscol->p_vartype,
                      nscol->p_vartypmod,
                      nscol->p_varcollid,
                      sublevels_up);
        /* makeVar doesn't offer parameters for these, so set them by hand: */
        var->varnosyn = nscol->p_varnosyn;
        var->varattnosyn = nscol->p_varattnosyn;
    }
    else
    {
        /* System column, so use predetermined type data */
        const FormData_pg_attribute *sysatt;

        sysatt = SystemAttributeDefinition(attnum);
        var = makeVar(nsitem->p_rtindex,
                      attnum,
                      sysatt->atttypid,
                      sysatt->atttypmod,
                      sysatt->attcollation,
                      sublevels_up);
    }
    var->location = location;

    /* Require read access to the column */
    markVarForSelectPriv(pstate, var, rte);

    return (Node *) var;
}

/*
 * scanRTEForColumn
 *    Search the column names of a single RTE for the given name.
 *    If found, return the attnum (possibly negative, for a system column);
 *    else return InvalidAttrNumber.
 *    If the name proves ambiguous within this RTE, raise error.
 *
 * pstate and location are passed only for error-reporting purposes.
 *
 * Side effect: if fuzzystate is non-NULL, check non-system columns
 * for an approximate match and update fuzzystate accordingly.
 *
 * Note: this is factored out of scanNSItemForColumn because error message
 * creation may want to check RTEs that are not in the namespace.  To support
 * that usage, minimize the number of validity checks performed here.  It's
 * okay to complain about ambiguous-name cases, though, since if we are
 * working to complain about an invalid name, we've already eliminated that.
 */
static int
scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte,
                 const char *colname, int location,
                 int fuzzy_rte_penalty,
                 FuzzyAttrMatchState *fuzzystate)
{
    int         result = InvalidAttrNumber;
    int         attnum = 0;
    ListCell   *c;

    /*
     * Scan the user column names (or aliases) for a match. Complain if
     * multiple matches.
     *
     * Note: eref->colnames may include entries for dropped columns, but those
     * will be empty strings that cannot match any legal SQL identifier, so we
     * don't bother to test for that case here.
     *
     * Should this somehow go wrong and we try to access a dropped column,
     * we'll still catch it by virtue of the check in scanNSItemForColumn().
     * Callers interested in finding match with shortest distance need to
     * defend against this directly, though.
     */
    foreach(c, rte->eref->colnames)
    {
        const char *attcolname = strVal(lfirst(c));

        attnum++;
        if (strcmp(attcolname, colname) == 0)
        {
            if (result)
                ereport(ERROR,
                        (errcode(ERRCODE_AMBIGUOUS_COLUMN),
                         errmsg("column reference \"%s\" is ambiguous",
                                colname),
                         parser_errposition(pstate, location)));
            result = attnum;
        }

        /* Update fuzzy match state, if provided. */
        if (fuzzystate != NULL)
            updateFuzzyAttrMatchState(fuzzy_rte_penalty, fuzzystate,
                                      rte, attcolname, colname, attnum);
    }

    /*
     * If we have a unique match, return it.  Note that this allows a user
     * alias to override a system column name (such as OID) without error.
     */
    if (result)
        return result;

    /*
     * If the RTE represents a real relation, consider system column names.
     * Composites are only used for pseudo-relations like ON CONFLICT's
     * excluded.
     */
    if (rte->rtekind == RTE_RELATION &&
        rte->relkind != RELKIND_COMPOSITE_TYPE)
    {
        /* quick check to see if name could be a system column */
        attnum = specialAttNum(colname);
        if (attnum != InvalidAttrNumber)
        {
            /* now check to see if column actually is defined */
            if (SearchSysCacheExists2(ATTNUM,
                                      ObjectIdGetDatum(rte->relid),
                                      Int16GetDatum(attnum)))
                result = attnum;
        }
    }

    return result;
}

/*
 * colNameToVar
 *    Search for an unqualified column name.
 *    If found, return the appropriate Var node (or expression).
 *    If not found, return NULL.  If the name proves ambiguous, raise error.
 *    If localonly is true, only names in the innermost query are considered.
 */
Node *
colNameToVar(ParseState *pstate, const char *colname, bool localonly,
             int location)
{
    Node       *result = NULL;
    int         sublevels_up = 0;
    ParseState *orig_pstate = pstate;

    while (pstate != NULL)
    {
        ListCell   *l;

        foreach(l, pstate->p_namespace)
        {
            ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(l);
            Node       *newresult;

            /* Ignore table-only items */
            if (!nsitem->p_cols_visible)
                continue;
            /* If not inside LATERAL, ignore lateral-only items */
            if (nsitem->p_lateral_only && !pstate->p_lateral_active)
                continue;

            /* use orig_pstate here for consistency with other callers */
            newresult = scanNSItemForColumn(orig_pstate, nsitem, sublevels_up,
                                            colname, location);

            if (newresult)
            {
                if (result)
                    ereport(ERROR,
                            (errcode(ERRCODE_AMBIGUOUS_COLUMN),
                             errmsg("column reference \"%s\" is ambiguous",
                                    colname),
                             parser_errposition(pstate, location)));
                check_lateral_ref_ok(pstate, nsitem, location);
                result = newresult;
            }
        }

        if (result != NULL || localonly)
            break;              /* found, or don't want to look at parent */

        pstate = pstate->parentParseState;
        sublevels_up++;
    }

    return result;
}

/*
 * searchRangeTableForCol
 *    See if any RangeTblEntry could possibly provide the given column name (or
 *    find the best match available).  Returns state with relevant details.
 *
 * This is different from colNameToVar in that it considers every entry in
 * the ParseState's rangetable(s), not only those that are currently visible
 * in the p_namespace list(s).  This behavior is invalid per the SQL spec,
 * and it may give ambiguous results (there might be multiple equally valid
 * matches, but only one will be returned).  This must be used ONLY as a
 * heuristic in giving suitable error messages.  See errorMissingColumn.
 *
 * This function is also different in that it will consider approximate
 * matches -- if the user entered an alias/column pair that is only slightly
 * different from a valid pair, we may be able to infer what they meant to
 * type and provide a reasonable hint.
 *
 * The FuzzyAttrMatchState will have 'rfirst' pointing to the best RTE
 * containing the most promising match for the alias and column name.  If
 * the alias and column names match exactly, 'first' will be InvalidAttrNumber;
 * otherwise, it will be the attribute number for the match.  In the latter
 * case, 'rsecond' may point to a second, equally close approximate match,
 * and 'second' will contain the attribute number for the second match.
 */
static FuzzyAttrMatchState *
searchRangeTableForCol(ParseState *pstate, const char *alias, const char *colname,
                       int location)
{
    ParseState *orig_pstate = pstate;
    FuzzyAttrMatchState *fuzzystate = palloc(sizeof(FuzzyAttrMatchState));

    fuzzystate->distance = MAX_FUZZY_DISTANCE + 1;
    fuzzystate->rfirst = NULL;
    fuzzystate->rsecond = NULL;
    fuzzystate->first = InvalidAttrNumber;
    fuzzystate->second = InvalidAttrNumber;

    while (pstate != NULL)
    {
        ListCell   *l;

        foreach(l, pstate->p_rtable)
        {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
            int         fuzzy_rte_penalty = 0;

            /*
             * Typically, it is not useful to look for matches within join
             * RTEs; they effectively duplicate other RTEs for our purposes,
             * and if a match is chosen from a join RTE, an unhelpful alias is
             * displayed in the final diagnostic message.
             */
            if (rte->rtekind == RTE_JOIN)
                continue;

            /*
             * If the user didn't specify an alias, then matches against one
             * RTE are as good as another.  But if the user did specify an
             * alias, then we want at least a fuzzy - and preferably an exact
             * - match for the range table entry.
             */
            if (alias != NULL)
                fuzzy_rte_penalty =
                    varstr_levenshtein_less_equal(alias, strlen(alias),
                                                  rte->eref->aliasname,
                                                  strlen(rte->eref->aliasname),
                                                  1, 1, 1,
                                                  MAX_FUZZY_DISTANCE + 1,
                                                  true);

            /*
             * Scan for a matching column; if we find an exact match, we're
             * done.  Otherwise, update fuzzystate.
             */
            if (scanRTEForColumn(orig_pstate, rte, colname, location,
                                 fuzzy_rte_penalty, fuzzystate)
                && fuzzy_rte_penalty == 0)
            {
                fuzzystate->rfirst = rte;
                fuzzystate->first = InvalidAttrNumber;
                fuzzystate->rsecond = NULL;
                fuzzystate->second = InvalidAttrNumber;
                return fuzzystate;
            }
        }

        pstate = pstate->parentParseState;
    }

    return fuzzystate;
}

/*
 * markRTEForSelectPriv
 *     Mark the specified column of an RTE as requiring SELECT privilege
 *
 * col == InvalidAttrNumber means a "whole row" reference
 *
 * External callers should always pass the Var's RTE.  Internally, we
 * allow NULL to be passed for the RTE and then look it up if needed;
 * this takes less code than requiring each internal recursion site
 * to perform a lookup.
 */
static void
markRTEForSelectPriv(ParseState *pstate, RangeTblEntry *rte,
                     int rtindex, AttrNumber col)
{
    if (rte == NULL)
        rte = rt_fetch(rtindex, pstate->p_rtable);

    if (rte->rtekind == RTE_RELATION)
    {
        /* Make sure the rel as a whole is marked for SELECT access */
        rte->requiredPerms |= ACL_SELECT;
        /* Must offset the attnum to fit in a bitmapset */
        rte->selectedCols = bms_add_member(rte->selectedCols,
                                           col - FirstLowInvalidHeapAttributeNumber);
    }
    else if (rte->rtekind == RTE_JOIN)
    {
        if (col == InvalidAttrNumber)
        {
            /*
             * A whole-row reference to a join has to be treated as whole-row
             * references to the two inputs.
             */
            JoinExpr   *j;

            if (rtindex > 0 && rtindex <= list_length(pstate->p_joinexprs))
                j = list_nth_node(JoinExpr, pstate->p_joinexprs, rtindex - 1);
            else
                j = NULL;
            if (j == NULL)
                elog(ERROR, "could not find JoinExpr for whole-row reference");

            /* Note: we can't see FromExpr here */
            if (IsA(j->larg, RangeTblRef))
            {
                int         varno = ((RangeTblRef *) j->larg)->rtindex;

                markRTEForSelectPriv(pstate, NULL, varno, InvalidAttrNumber);
            }
            else if (IsA(j->larg, JoinExpr))
            {
                int         varno = ((JoinExpr *) j->larg)->rtindex;

                markRTEForSelectPriv(pstate, NULL, varno, InvalidAttrNumber);
            }
            else
                elog(ERROR, "unrecognized node type: %d",
                     (int) nodeTag(j->larg));
            if (IsA(j->rarg, RangeTblRef))
            {
                int         varno = ((RangeTblRef *) j->rarg)->rtindex;

                markRTEForSelectPriv(pstate, NULL, varno, InvalidAttrNumber);
            }
            else if (IsA(j->rarg, JoinExpr))
            {
                int         varno = ((JoinExpr *) j->rarg)->rtindex;

                markRTEForSelectPriv(pstate, NULL, varno, InvalidAttrNumber);
            }
            else
                elog(ERROR, "unrecognized node type: %d",
                     (int) nodeTag(j->rarg));
        }
        else
        {
            /*
             * Join alias Vars for ordinary columns must refer to merged JOIN
             * USING columns.  We don't need to do anything here, because the
             * join input columns will also be referenced in the join's qual
             * clause, and will get marked for select privilege there.
             */
        }
    }
    /* other RTE types don't require privilege marking */
}

/*
 * markVarForSelectPriv
 *     Mark the RTE referenced by a Var as requiring SELECT privilege
 */
void
markVarForSelectPriv(ParseState *pstate, Var *var, RangeTblEntry *rte)
{
    Index       lv;

    Assert(IsA(var, Var));
    /* Find the appropriate pstate if it's an uplevel Var */
    for (lv = 0; lv < var->varlevelsup; lv++)
        pstate = pstate->parentParseState;
    markRTEForSelectPriv(pstate, rte, var->varno, var->varattno);
}

/*
 * buildRelationAliases
 *      Construct the eref column name list for a relation RTE.
 *      This code is also used for function RTEs.
 *
 * tupdesc: the physical column information
 * alias: the user-supplied alias, or NULL if none
 * eref: the eref Alias to store column names in
 *
 * eref->colnames is filled in.  Also, alias->colnames is rebuilt to insert
 * empty strings for any dropped columns, so that it will be one-to-one with
 * physical column numbers.
 *
 * It is an error for there to be more aliases present than required.
 */
static void
buildRelationAliases(TupleDesc tupdesc, Alias *alias, Alias *eref)
{
    int         maxattrs = tupdesc->natts;
    List       *aliaslist;
    ListCell   *aliaslc;
    int         numaliases;
    int         varattno;
    int         numdropped = 0;

    Assert(eref->colnames == NIL);

    if (alias)
    {
        aliaslist = alias->colnames;
        aliaslc = list_head(aliaslist);
        numaliases = list_length(aliaslist);
        /* We'll rebuild the alias colname list */
        alias->colnames = NIL;
    }
    else
    {
        aliaslist = NIL;
        aliaslc = NULL;
        numaliases = 0;
    }

    for (varattno = 0; varattno < maxattrs; varattno++)
    {
        Form_pg_attribute attr = TupleDescAttr(tupdesc, varattno);
        Value      *attrname;

        if (attr->attisdropped)
        {
            /* Always insert an empty string for a dropped column */
            attrname = makeString(pstrdup(""));
            if (aliaslc)
                alias->colnames = lappend(alias->colnames, attrname);
            numdropped++;
        }
        else if (aliaslc)
        {
            /* Use the next user-supplied alias */
            attrname = (Value *) lfirst(aliaslc);
            aliaslc = lnext(aliaslist, aliaslc);
            alias->colnames = lappend(alias->colnames, attrname);
        }
        else
        {
            attrname = makeString(pstrdup(NameStr(attr->attname)));
            /* we're done with the alias if any */
        }

        eref->colnames = lappend(eref->colnames, attrname);
    }

    /* Too many user-supplied aliases? */
    if (aliaslc)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("table \"%s\" has %d columns available but %d columns specified",
                        eref->aliasname, maxattrs - numdropped, numaliases)));
}

/*
 * chooseScalarFunctionAlias
 *      Select the column alias for a function in a function RTE,
 *      when the function returns a scalar type (not composite or RECORD).
 *
 * funcexpr: transformed expression tree for the function call
 * funcname: function name (as determined by FigureColname)
 * alias: the user-supplied alias for the RTE, or NULL if none
 * nfuncs: the number of functions appearing in the function RTE
 *
 * Note that the name we choose might be overridden later, if the user-given
 * alias includes column alias names.  That's of no concern here.
 */
static char *
chooseScalarFunctionAlias(Node *funcexpr, char *funcname,
                          Alias *alias, int nfuncs)
{
    char       *pname;

    /*
     * If the expression is a simple function call, and the function has a
     * single OUT parameter that is named, use the parameter's name.
     */
    if (funcexpr && IsA(funcexpr, FuncExpr))
    {
        pname = get_func_result_name(((FuncExpr *) funcexpr)->funcid);
        if (pname)
            return pname;
    }

    /*
     * If there's just one function in the RTE, and the user gave an RTE alias
     * name, use that name.  (This makes FROM func() AS foo use "foo" as the
     * column name as well as the table alias.)
     */
    if (nfuncs == 1 && alias)
        return alias->aliasname;

    /*
     * Otherwise use the function name.
     */
    return funcname;
}

/*
 * buildNSItemFromTupleDesc
 *      Build a ParseNamespaceItem, given a tupdesc describing the columns.
 *
 * rte: the new RangeTblEntry for the rel
 * rtindex: its index in the rangetable list
 * tupdesc: the physical column information
 */
static ParseNamespaceItem *
buildNSItemFromTupleDesc(RangeTblEntry *rte, Index rtindex, TupleDesc tupdesc)
{
    ParseNamespaceItem *nsitem;
    ParseNamespaceColumn *nscolumns;
    int         maxattrs = tupdesc->natts;
    int         varattno;

    /* colnames must have the same number of entries as the nsitem */
    Assert(maxattrs == list_length(rte->eref->colnames));

    /* extract per-column data from the tupdesc */
    nscolumns = (ParseNamespaceColumn *)
        palloc0(maxattrs * sizeof(ParseNamespaceColumn));

    for (varattno = 0; varattno < maxattrs; varattno++)
    {
        Form_pg_attribute attr = TupleDescAttr(tupdesc, varattno);

        /* For a dropped column, just leave the entry as zeroes */
        if (attr->attisdropped)
            continue;

        nscolumns[varattno].p_varno = rtindex;
        nscolumns[varattno].p_varattno = varattno + 1;
        nscolumns[varattno].p_vartype = attr->atttypid;
        nscolumns[varattno].p_vartypmod = attr->atttypmod;
        nscolumns[varattno].p_varcollid = attr->attcollation;
        nscolumns[varattno].p_varnosyn = rtindex;
        nscolumns[varattno].p_varattnosyn = varattno + 1;
    }

    /* ... and build the nsitem */
    nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
    nsitem->p_rte = rte;
    nsitem->p_rtindex = rtindex;
    nsitem->p_nscolumns = nscolumns;
    /* set default visibility flags; might get changed later */
    nsitem->p_rel_visible = true;
    nsitem->p_cols_visible = true;
    nsitem->p_lateral_only = false;
    nsitem->p_lateral_ok = true;

    return nsitem;
}

/*
 * buildNSItemFromLists
 *      Build a ParseNamespaceItem, given column type information in lists.
 *
 * rte: the new RangeTblEntry for the rel
 * rtindex: its index in the rangetable list
 * coltypes: per-column datatype OIDs
 * coltypmods: per-column type modifiers
 * colcollation: per-column collation OIDs
 */
static ParseNamespaceItem *
buildNSItemFromLists(RangeTblEntry *rte, Index rtindex,
                     List *coltypes, List *coltypmods, List *colcollations)
{
    ParseNamespaceItem *nsitem;
    ParseNamespaceColumn *nscolumns;
    int         maxattrs = list_length(coltypes);
    int         varattno;
    ListCell   *lct;
    ListCell   *lcm;
    ListCell   *lcc;

    /* colnames must have the same number of entries as the nsitem */
    Assert(maxattrs == list_length(rte->eref->colnames));

    Assert(maxattrs == list_length(coltypmods));
    Assert(maxattrs == list_length(colcollations));

    /* extract per-column data from the lists */
    nscolumns = (ParseNamespaceColumn *)
        palloc0(maxattrs * sizeof(ParseNamespaceColumn));

    varattno = 0;
    forthree(lct, coltypes,
             lcm, coltypmods,
             lcc, colcollations)
    {
        nscolumns[varattno].p_varno = rtindex;
        nscolumns[varattno].p_varattno = varattno + 1;
        nscolumns[varattno].p_vartype = lfirst_oid(lct);
        nscolumns[varattno].p_vartypmod = lfirst_int(lcm);
        nscolumns[varattno].p_varcollid = lfirst_oid(lcc);
        nscolumns[varattno].p_varnosyn = rtindex;
        nscolumns[varattno].p_varattnosyn = varattno + 1;
        varattno++;
    }

    /* ... and build the nsitem */
    nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
    nsitem->p_rte = rte;
    nsitem->p_rtindex = rtindex;
    nsitem->p_nscolumns = nscolumns;
    /* set default visibility flags; might get changed later */
    nsitem->p_rel_visible = true;
    nsitem->p_cols_visible = true;
    nsitem->p_lateral_only = false;
    nsitem->p_lateral_ok = true;

    return nsitem;
}

/*
 * Open a table during parse analysis
 *
 * This is essentially just the same as table_openrv(), except that it caters
 * to some parser-specific error reporting needs, notably that it arranges
 * to include the RangeVar's parse location in any resulting error.
 *
 * Note: properly, lockmode should be declared LOCKMODE not int, but that
 * would require importing storage/lock.h into parse_relation.h.  Since
 * LOCKMODE is typedef'd as int anyway, that seems like overkill.
 */
Relation
parserOpenTable(ParseState *pstate, const RangeVar *relation, int lockmode)
{
    Relation    rel;
    ParseCallbackState pcbstate;

    setup_parser_errposition_callback(&pcbstate, pstate, relation->location);
    rel = table_openrv_extended(relation, lockmode, true);
    if (rel == NULL)
    {
        if (relation->schemaname)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_TABLE),
                     errmsg("relation \"%s.%s\" does not exist",
                            relation->schemaname, relation->relname)));
        else
        {
            /*
             * An unqualified name might have been meant as a reference to
             * some not-yet-in-scope CTE.  The bare "does not exist" message
             * has proven remarkably unhelpful for figuring out such problems,
             * so we take pains to offer a specific hint.
             */
            if (isFutureCTE(pstate, relation->relname))
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_TABLE),
                         errmsg("relation \"%s\" does not exist",
                                relation->relname),
                         errdetail("There is a WITH item named \"%s\", but it cannot be referenced from this part of the query.",
                                   relation->relname),
                         errhint("Use WITH RECURSIVE, or re-order the WITH items to remove forward references.")));
            else
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_TABLE),
                         errmsg("relation \"%s\" does not exist",
                                relation->relname)));
        }
    }
    cancel_parser_errposition_callback(&pcbstate);
    return rel;
}

/*
 * Add an entry for a relation to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * We do not link the ParseNamespaceItem into the pstate here; it's the
 * caller's job to do that in the appropriate way.
 *
 * Note: formerly this checked for refname conflicts, but that's wrong.
 * Caller is responsible for checking for conflicts in the appropriate scope.
 */
ParseNamespaceItem *
addRangeTableEntry(ParseState *pstate,
                   RangeVar *relation,
                   Alias *alias,
                   bool inh,
                   bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    char       *refname = alias ? alias->aliasname : relation->relname;
    LOCKMODE    lockmode;
    Relation    rel;
    ParseNamespaceItem *nsitem;

    Assert(pstate != NULL);

    rte->rtekind = RTE_RELATION;
    rte->alias = alias;

    /*
     * Identify the type of lock we'll need on this relation.  It's not the
     * query's target table (that case is handled elsewhere), so we need
     * either RowShareLock if it's locked by FOR UPDATE/SHARE, or plain
     * AccessShareLock otherwise.
     */
    lockmode = isLockedRefname(pstate, refname) ? RowShareLock : AccessShareLock;

    /*
     * Get the rel's OID.  This access also ensures that we have an up-to-date
     * relcache entry for the rel.  Since this is typically the first access
     * to a rel in a statement, we must open the rel with the proper lockmode.
     */
    rel = parserOpenTable(pstate, relation, lockmode);
    rte->relid = RelationGetRelid(rel);
    rte->relkind = rel->rd_rel->relkind;
    rte->rellockmode = lockmode;

    /*
     * Build the list of effective column names using user-supplied aliases
     * and/or actual column names.
     */
    rte->eref = makeAlias(refname, NIL);
    buildRelationAliases(rel->rd_att, alias, rte->eref);

    /*
     * Set flags and access permissions.
     *
     * The initial default on access checks is always check-for-READ-access,
     * which is the right thing for all except target tables.
     */
    rte->lateral = false;
    rte->inh = inh;
    rte->inFromCl = inFromCl;

    rte->requiredPerms = ACL_SELECT;
    rte->checkAsUser = InvalidOid;  /* not set-uid by default, either */
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    nsitem = buildNSItemFromTupleDesc(rte, list_length(pstate->p_rtable),
                                      rel->rd_att);

    /*
     * Drop the rel refcount, but keep the access lock till end of transaction
     * so that the table can't be deleted or have its schema modified
     * underneath us.
     */
    table_close(rel, NoLock);

    return nsitem;
}

/*
 * Add an entry for a relation to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is just like addRangeTableEntry() except that it makes an RTE
 * given an already-open relation instead of a RangeVar reference.
 *
 * lockmode is the lock type required for query execution; it must be one
 * of AccessShareLock, RowShareLock, or RowExclusiveLock depending on the
 * RTE's role within the query.  The caller must hold that lock mode
 * or a stronger one.
 *
 * Note: properly, lockmode should be declared LOCKMODE not int, but that
 * would require importing storage/lock.h into parse_relation.h.  Since
 * LOCKMODE is typedef'd as int anyway, that seems like overkill.
 */
ParseNamespaceItem *
addRangeTableEntryForRelation(ParseState *pstate,
                              Relation rel,
                              int lockmode,
                              Alias *alias,
                              bool inh,
                              bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    char       *refname = alias ? alias->aliasname : RelationGetRelationName(rel);

    Assert(pstate != NULL);

    Assert(lockmode == AccessShareLock ||
           lockmode == RowShareLock ||
           lockmode == RowExclusiveLock);
    Assert(CheckRelationLockedByMe(rel, lockmode, true));

    rte->rtekind = RTE_RELATION;
    rte->alias = alias;
    rte->relid = RelationGetRelid(rel);
    rte->relkind = rel->rd_rel->relkind;
    rte->rellockmode = lockmode;

    /*
     * Build the list of effective column names using user-supplied aliases
     * and/or actual column names.
     */
    rte->eref = makeAlias(refname, NIL);
    buildRelationAliases(rel->rd_att, alias, rte->eref);

    /*
     * Set flags and access permissions.
     *
     * The initial default on access checks is always check-for-READ-access,
     * which is the right thing for all except target tables.
     */
    rte->lateral = false;
    rte->inh = inh;
    rte->inFromCl = inFromCl;

    rte->requiredPerms = ACL_SELECT;
    rte->checkAsUser = InvalidOid;  /* not set-uid by default, either */
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromTupleDesc(rte, list_length(pstate->p_rtable),
                                    rel->rd_att);
}

/*
 * Add an entry for a subquery to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a subquery RTE.
 * Note that an alias clause *must* be supplied.
 */
ParseNamespaceItem *
addRangeTableEntryForSubquery(ParseState *pstate,
                              Query *subquery,
                              Alias *alias,
                              bool lateral,
                              bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    char       *refname = alias->aliasname;
    Alias      *eref;
    int         numaliases;
    List       *coltypes,
               *coltypmods,
               *colcollations;
    int         varattno;
    ListCell   *tlistitem;

    Assert(pstate != NULL);

    rte->rtekind = RTE_SUBQUERY;
    rte->subquery = subquery;
    rte->alias = alias;

    eref = copyObject(alias);
    numaliases = list_length(eref->colnames);

    /* fill in any unspecified alias columns, and extract column type info */
    coltypes = coltypmods = colcollations = NIL;
    varattno = 0;
    foreach(tlistitem, subquery->targetList)
    {
        TargetEntry *te = (TargetEntry *) lfirst(tlistitem);

        if (te->resjunk)
            continue;
        varattno++;
        Assert(varattno == te->resno);
        if (varattno > numaliases)
        {
            char       *attrname;

            attrname = pstrdup(te->resname);
            eref->colnames = lappend(eref->colnames, makeString(attrname));
        }
        coltypes = lappend_oid(coltypes,
                               exprType((Node *) te->expr));
        coltypmods = lappend_int(coltypmods,
                                 exprTypmod((Node *) te->expr));
        colcollations = lappend_oid(colcollations,
                                    exprCollation((Node *) te->expr));
    }
    if (varattno < numaliases)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("table \"%s\" has %d columns available but %d columns specified",
                        refname, varattno, numaliases)));

    rte->eref = eref;

    /*
     * Set flags and access permissions.
     *
     * Subqueries are never checked for access rights.
     */
    rte->lateral = lateral;
    rte->inh = false;           /* never true for subqueries */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromLists(rte, list_length(pstate->p_rtable),
                                coltypes, coltypmods, colcollations);
}

/*
 * Add an entry for a function (or functions) to the pstate's range table
 * (p_rtable).  Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a function RTE.
 */
ParseNamespaceItem *
addRangeTableEntryForFunction(ParseState *pstate,
                              List *funcnames,
                              List *funcexprs,
                              List *coldeflists,
                              RangeFunction *rangefunc,
                              bool lateral,
                              bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    Alias      *alias = rangefunc->alias;
    Alias      *eref;
    char       *aliasname;
    int         nfuncs = list_length(funcexprs);
    TupleDesc  *functupdescs;
    TupleDesc   tupdesc;
    ListCell   *lc1,
               *lc2,
               *lc3;
    int         i;
    int         j;
    int         funcno;
    int         natts,
                totalatts;

    Assert(pstate != NULL);

    rte->rtekind = RTE_FUNCTION;
    rte->relid = InvalidOid;
    rte->subquery = NULL;
    rte->functions = NIL;       /* we'll fill this list below */
    rte->funcordinality = rangefunc->ordinality;
    rte->alias = alias;

    /*
     * Choose the RTE alias name.  We default to using the first function's
     * name even when there's more than one; which is maybe arguable but beats
     * using something constant like "table".
     */
    if (alias)
        aliasname = alias->aliasname;
    else
        aliasname = linitial(funcnames);

    eref = makeAlias(aliasname, NIL);
    rte->eref = eref;

    /* Process each function ... */
    functupdescs = (TupleDesc *) palloc(nfuncs * sizeof(TupleDesc));

    totalatts = 0;
    funcno = 0;
    forthree(lc1, funcexprs, lc2, funcnames, lc3, coldeflists)
    {
        Node       *funcexpr = (Node *) lfirst(lc1);
        char       *funcname = (char *) lfirst(lc2);
        List       *coldeflist = (List *) lfirst(lc3);
        RangeTblFunction *rtfunc = makeNode(RangeTblFunction);
        TypeFuncClass functypclass;
        Oid         funcrettype;

        /* Initialize RangeTblFunction node */
        rtfunc->funcexpr = funcexpr;
        rtfunc->funccolnames = NIL;
        rtfunc->funccoltypes = NIL;
        rtfunc->funccoltypmods = NIL;
        rtfunc->funccolcollations = NIL;
        rtfunc->funcparams = NULL;  /* not set until planning */

        /*
         * Now determine if the function returns a simple or composite type.
         */
        functypclass = get_expr_result_type(funcexpr,
                                            &funcrettype,
                                            &tupdesc);

        /*
         * A coldeflist is required if the function returns RECORD and hasn't
         * got a predetermined record type, and is prohibited otherwise.  This
         * can be a bit confusing, so we expend some effort on delivering a
         * relevant error message.
         */
        if (coldeflist != NIL)
        {
            switch (functypclass)
            {
                case TYPEFUNC_RECORD:
                    /* ok */
                    break;
                case TYPEFUNC_COMPOSITE:
                case TYPEFUNC_COMPOSITE_DOMAIN:

                    /*
                     * If the function's raw result type is RECORD, we must
                     * have resolved it using its OUT parameters.  Otherwise,
                     * it must have a named composite type.
                     */
                    if (exprType(funcexpr) == RECORDOID)
                        ereport(ERROR,
                                (errcode(ERRCODE_SYNTAX_ERROR),
                                 errmsg("a column definition list is redundant for a function with OUT parameters"),
                                 parser_errposition(pstate,
                                                    exprLocation((Node *) coldeflist))));
                    else
                        ereport(ERROR,
                                (errcode(ERRCODE_SYNTAX_ERROR),
                                 errmsg("a column definition list is redundant for a function returning a named composite type"),
                                 parser_errposition(pstate,
                                                    exprLocation((Node *) coldeflist))));
                    break;
                default:
                    ereport(ERROR,
                            (errcode(ERRCODE_SYNTAX_ERROR),
                             errmsg("a column definition list is only allowed for functions returning \"record\""),
                             parser_errposition(pstate,
                                                exprLocation((Node *) coldeflist))));
                    break;
            }
        }
        else
        {
            if (functypclass == TYPEFUNC_RECORD)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("a column definition list is required for functions returning \"record\""),
                         parser_errposition(pstate, exprLocation(funcexpr))));
        }

        if (functypclass == TYPEFUNC_COMPOSITE ||
            functypclass == TYPEFUNC_COMPOSITE_DOMAIN)
        {
            /* Composite data type, e.g. a table's row type */
            Assert(tupdesc);
        }
        else if (functypclass == TYPEFUNC_SCALAR)
        {
            /* Base data type, i.e. scalar */
            tupdesc = CreateTemplateTupleDesc(1);
            TupleDescInitEntry(tupdesc,
                               (AttrNumber) 1,
                               chooseScalarFunctionAlias(funcexpr, funcname,
                                                         alias, nfuncs),
                               funcrettype,
                               exprTypmod(funcexpr),
                               0);
            TupleDescInitEntryCollation(tupdesc,
                                        (AttrNumber) 1,
                                        exprCollation(funcexpr));
        }
        else if (functypclass == TYPEFUNC_RECORD)
        {
            ListCell   *col;

            /*
             * Use the column definition list to construct a tupdesc and fill
             * in the RangeTblFunction's lists.
             */
            tupdesc = CreateTemplateTupleDesc(list_length(coldeflist));
            i = 1;
            foreach(col, coldeflist)
            {
                ColumnDef  *n = (ColumnDef *) lfirst(col);
                char       *attrname;
                Oid         attrtype;
                int32       attrtypmod;
                Oid         attrcollation;

                attrname = n->colname;
                if (n->typeName->setof)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                             errmsg("column \"%s\" cannot be declared SETOF",
                                    attrname),
                             parser_errposition(pstate, n->location)));
                typenameTypeIdAndMod(pstate, n->typeName,
                                     &attrtype, &attrtypmod);
                attrcollation = GetColumnDefCollation(pstate, n, attrtype);
                TupleDescInitEntry(tupdesc,
                                   (AttrNumber) i,
                                   attrname,
                                   attrtype,
                                   attrtypmod,
                                   0);
                TupleDescInitEntryCollation(tupdesc,
                                            (AttrNumber) i,
                                            attrcollation);
                rtfunc->funccolnames = lappend(rtfunc->funccolnames,
                                               makeString(pstrdup(attrname)));
                rtfunc->funccoltypes = lappend_oid(rtfunc->funccoltypes,
                                                   attrtype);
                rtfunc->funccoltypmods = lappend_int(rtfunc->funccoltypmods,
                                                     attrtypmod);
                rtfunc->funccolcollations = lappend_oid(rtfunc->funccolcollations,
                                                        attrcollation);

                i++;
            }

            /*
             * Ensure that the coldeflist defines a legal set of names (no
             * duplicates, but we needn't worry about system column names) and
             * datatypes.  Although we mostly can't allow pseudo-types, it
             * seems safe to allow RECORD and RECORD[], since values within
             * those type classes are self-identifying at runtime, and the
             * coldeflist doesn't represent anything that will be visible to
             * other sessions.
             */
            CheckAttributeNamesTypes(tupdesc, RELKIND_COMPOSITE_TYPE,
                                     CHKATYPE_ANYRECORD);
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("function \"%s\" in FROM has unsupported return type %s",
                            funcname, format_type_be(funcrettype)),
                     parser_errposition(pstate, exprLocation(funcexpr))));

        /* Finish off the RangeTblFunction and add it to the RTE's list */
        rtfunc->funccolcount = tupdesc->natts;
        rte->functions = lappend(rte->functions, rtfunc);

        /* Save the tupdesc for use below */
        functupdescs[funcno] = tupdesc;
        totalatts += tupdesc->natts;
        funcno++;
    }

    /*
     * If there's more than one function, or we want an ordinality column, we
     * have to produce a merged tupdesc.
     */
    if (nfuncs > 1 || rangefunc->ordinality)
    {
        if (rangefunc->ordinality)
            totalatts++;

        /* Merge the tuple descs of each function into a composite one */
        tupdesc = CreateTemplateTupleDesc(totalatts);
        natts = 0;
        for (i = 0; i < nfuncs; i++)
        {
            for (j = 1; j <= functupdescs[i]->natts; j++)
                TupleDescCopyEntry(tupdesc, ++natts, functupdescs[i], j);
        }

        /* Add the ordinality column if needed */
        if (rangefunc->ordinality)
        {
            TupleDescInitEntry(tupdesc,
                               (AttrNumber) ++natts,
                               "ordinality",
                               INT8OID,
                               -1,
                               0);
            /* no need to set collation */
        }

        Assert(natts == totalatts);
    }
    else
    {
        /* We can just use the single function's tupdesc as-is */
        tupdesc = functupdescs[0];
    }

    /* Use the tupdesc while assigning column aliases for the RTE */
    buildRelationAliases(tupdesc, alias, eref);

    /*
     * Set flags and access permissions.
     *
     * Functions are never checked for access rights (at least, not by the RTE
     * permissions mechanism).
     */
    rte->lateral = lateral;
    rte->inh = false;           /* never true for functions */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromTupleDesc(rte, list_length(pstate->p_rtable),
                                    tupdesc);
}

/*
 * Add an entry for a table function to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a tablefunc RTE.
 */
ParseNamespaceItem *
addRangeTableEntryForTableFunc(ParseState *pstate,
                               TableFunc *tf,
                               Alias *alias,
                               bool lateral,
                               bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    char       *refname = alias ? alias->aliasname : pstrdup("xmltable");
    Alias      *eref;
    int         numaliases;

    Assert(pstate != NULL);

    rte->rtekind = RTE_TABLEFUNC;
    rte->relid = InvalidOid;
    rte->subquery = NULL;
    rte->tablefunc = tf;
    rte->coltypes = tf->coltypes;
    rte->coltypmods = tf->coltypmods;
    rte->colcollations = tf->colcollations;
    rte->alias = alias;

    eref = alias ? copyObject(alias) : makeAlias(refname, NIL);
    numaliases = list_length(eref->colnames);

    /* fill in any unspecified alias columns */
    if (numaliases < list_length(tf->colnames))
        eref->colnames = list_concat(eref->colnames,
                                     list_copy_tail(tf->colnames, numaliases));

    rte->eref = eref;

    /*
     * Set flags and access permissions.
     *
     * Tablefuncs are never checked for access rights (at least, not by the
     * RTE permissions mechanism).
     */
    rte->lateral = lateral;
    rte->inh = false;           /* never true for tablefunc RTEs */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromLists(rte, list_length(pstate->p_rtable),
                                rte->coltypes, rte->coltypmods,
                                rte->colcollations);
}

/*
 * Add an entry for a VALUES list to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a values RTE.
 */
ParseNamespaceItem *
addRangeTableEntryForValues(ParseState *pstate,
                            List *exprs,
                            List *coltypes,
                            List *coltypmods,
                            List *colcollations,
                            Alias *alias,
                            bool lateral,
                            bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    char       *refname = alias ? alias->aliasname : pstrdup("*VALUES*");
    Alias      *eref;
    int         numaliases;
    int         numcolumns;

    Assert(pstate != NULL);

    rte->rtekind = RTE_VALUES;
    rte->relid = InvalidOid;
    rte->subquery = NULL;
    rte->values_lists = exprs;
    rte->coltypes = coltypes;
    rte->coltypmods = coltypmods;
    rte->colcollations = colcollations;
    rte->alias = alias;

    eref = alias ? copyObject(alias) : makeAlias(refname, NIL);

    /* fill in any unspecified alias columns */
    numcolumns = list_length((List *) linitial(exprs));
    numaliases = list_length(eref->colnames);
    while (numaliases < numcolumns)
    {
        char        attrname[64];

        numaliases++;
        snprintf(attrname, sizeof(attrname), "column%d", numaliases);
        eref->colnames = lappend(eref->colnames,
                                 makeString(pstrdup(attrname)));
    }
    if (numcolumns < numaliases)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("VALUES lists \"%s\" have %d columns available but %d columns specified",
                        refname, numcolumns, numaliases)));

    rte->eref = eref;

    /*
     * Set flags and access permissions.
     *
     * Subqueries are never checked for access rights.
     */
    rte->lateral = lateral;
    rte->inh = false;           /* never true for values RTEs */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromLists(rte, list_length(pstate->p_rtable),
                                rte->coltypes, rte->coltypmods,
                                rte->colcollations);
}

/*
 * Add an entry for a join to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a join RTE.
 * Also, it's more convenient for the caller to construct the
 * ParseNamespaceColumn array, so we pass that in.
 */
ParseNamespaceItem *
addRangeTableEntryForJoin(ParseState *pstate,
                          List *colnames,
                          ParseNamespaceColumn *nscolumns,
                          JoinType jointype,
                          int nummergedcols,
                          List *aliasvars,
                          List *leftcols,
                          List *rightcols,
                          Alias *alias,
                          bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    Alias      *eref;
    int         numaliases;
    ParseNamespaceItem *nsitem;

    Assert(pstate != NULL);

    /*
     * Fail if join has too many columns --- we must be able to reference any
     * of the columns with an AttrNumber.
     */
    if (list_length(aliasvars) > MaxAttrNumber)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("joins can have at most %d columns",
                        MaxAttrNumber)));

    rte->rtekind = RTE_JOIN;
    rte->relid = InvalidOid;
    rte->subquery = NULL;
    rte->jointype = jointype;
    rte->joinmergedcols = nummergedcols;
    rte->joinaliasvars = aliasvars;
    rte->joinleftcols = leftcols;
    rte->joinrightcols = rightcols;
    rte->alias = alias;

    eref = alias ? copyObject(alias) : makeAlias("unnamed_join", NIL);
    numaliases = list_length(eref->colnames);

    /* fill in any unspecified alias columns */
    if (numaliases < list_length(colnames))
        eref->colnames = list_concat(eref->colnames,
                                     list_copy_tail(colnames, numaliases));

    rte->eref = eref;

    /*
     * Set flags and access permissions.
     *
     * Joins are never checked for access rights.
     */
    rte->lateral = false;
    rte->inh = false;           /* never true for joins */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
    nsitem->p_rte = rte;
    nsitem->p_rtindex = list_length(pstate->p_rtable);
    nsitem->p_nscolumns = nscolumns;
    /* set default visibility flags; might get changed later */
    nsitem->p_rel_visible = true;
    nsitem->p_cols_visible = true;
    nsitem->p_lateral_only = false;
    nsitem->p_lateral_ok = true;

    return nsitem;
}

/*
 * Add an entry for a CTE reference to the pstate's range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * This is much like addRangeTableEntry() except that it makes a CTE RTE.
 */
ParseNamespaceItem *
addRangeTableEntryForCTE(ParseState *pstate,
                         CommonTableExpr *cte,
                         Index levelsup,
                         RangeVar *rv,
                         bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    Alias      *alias = rv->alias;
    char       *refname = alias ? alias->aliasname : cte->ctename;
    Alias      *eref;
    int         numaliases;
    int         varattno;
    ListCell   *lc;

    Assert(pstate != NULL);

    rte->rtekind = RTE_CTE;
    rte->ctename = cte->ctename;
    rte->ctelevelsup = levelsup;

    /* Self-reference if and only if CTE's parse analysis isn't completed */
    rte->self_reference = !IsA(cte->ctequery, Query);
    Assert(cte->cterecursive || !rte->self_reference);
    /* Bump the CTE's refcount if this isn't a self-reference */
    if (!rte->self_reference)
        cte->cterefcount++;

    /*
     * We throw error if the CTE is INSERT/UPDATE/DELETE without RETURNING.
     * This won't get checked in case of a self-reference, but that's OK
     * because data-modifying CTEs aren't allowed to be recursive anyhow.
     */
    if (IsA(cte->ctequery, Query))
    {
        Query      *ctequery = (Query *) cte->ctequery;

        if (ctequery->commandType != CMD_SELECT &&
            ctequery->returningList == NIL)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("WITH query \"%s\" does not have a RETURNING clause",
                            cte->ctename),
                     parser_errposition(pstate, rv->location)));
    }

    rte->coltypes = cte->ctecoltypes;
    rte->coltypmods = cte->ctecoltypmods;
    rte->colcollations = cte->ctecolcollations;

    rte->alias = alias;
    if (alias)
        eref = copyObject(alias);
    else
        eref = makeAlias(refname, NIL);
    numaliases = list_length(eref->colnames);

    /* fill in any unspecified alias columns */
    varattno = 0;
    foreach(lc, cte->ctecolnames)
    {
        varattno++;
        if (varattno > numaliases)
            eref->colnames = lappend(eref->colnames, lfirst(lc));
    }
    if (varattno < numaliases)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                 errmsg("table \"%s\" has %d columns available but %d columns specified",
                        refname, varattno, numaliases)));

    rte->eref = eref;

    /*
     * Set flags and access permissions.
     *
     * Subqueries are never checked for access rights.
     */
    rte->lateral = false;
    rte->inh = false;           /* never true for subqueries */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;
    rte->insertedCols = NULL;
    rte->updatedCols = NULL;
    rte->extraUpdatedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromLists(rte, list_length(pstate->p_rtable),
                                rte->coltypes, rte->coltypmods,
                                rte->colcollations);
}

/*
 * Add an entry for an ephemeral named relation reference to the pstate's
 * range table (p_rtable).
 * Then, construct and return a ParseNamespaceItem for the new RTE.
 *
 * It is expected that the RangeVar, which up until now is only known to be an
 * ephemeral named relation, will (in conjunction with the QueryEnvironment in
 * the ParseState), create a RangeTblEntry for a specific *kind* of ephemeral
 * named relation, based on enrtype.
 *
 * This is much like addRangeTableEntry() except that it makes an RTE for an
 * ephemeral named relation.
 */
ParseNamespaceItem *
addRangeTableEntryForENR(ParseState *pstate,
                         RangeVar *rv,
                         bool inFromCl)
{
    RangeTblEntry *rte = makeNode(RangeTblEntry);
    Alias      *alias = rv->alias;
    char       *refname = alias ? alias->aliasname : rv->relname;
    EphemeralNamedRelationMetadata enrmd;
    TupleDesc   tupdesc;
    int         attno;

    Assert(pstate != NULL);
    enrmd = get_visible_ENR(pstate, rv->relname);
    Assert(enrmd != NULL);

    switch (enrmd->enrtype)
    {
        case ENR_NAMED_TUPLESTORE:
            rte->rtekind = RTE_NAMEDTUPLESTORE;
            break;

        default:
            elog(ERROR, "unexpected enrtype: %d", enrmd->enrtype);
            return NULL;        /* for fussy compilers */
    }

    /*
     * Record dependency on a relation.  This allows plans to be invalidated
     * if they access transition tables linked to a table that is altered.
     */
    rte->relid = enrmd->reliddesc;

    /*
     * Build the list of effective column names using user-supplied aliases
     * and/or actual column names.
     */
    tupdesc = ENRMetadataGetTupDesc(enrmd);
    rte->eref = makeAlias(refname, NIL);
    buildRelationAliases(tupdesc, alias, rte->eref);

    /* Record additional data for ENR, including column type info */
    rte->enrname = enrmd->name;
    rte->enrtuples = enrmd->enrtuples;
    rte->coltypes = NIL;
    rte->coltypmods = NIL;
    rte->colcollations = NIL;
    for (attno = 1; attno <= tupdesc->natts; ++attno)
    {
        Form_pg_attribute att = TupleDescAttr(tupdesc, attno - 1);

        if (att->attisdropped)
        {
            /* Record zeroes for a dropped column */
            rte->coltypes = lappend_oid(rte->coltypes, InvalidOid);
            rte->coltypmods = lappend_int(rte->coltypmods, 0);
            rte->colcollations = lappend_oid(rte->colcollations, InvalidOid);
        }
        else
        {
            /* Let's just make sure we can tell this isn't dropped */
            if (att->atttypid == InvalidOid)
                elog(ERROR, "atttypid is invalid for non-dropped column in \"%s\"",
                     rv->relname);
            rte->coltypes = lappend_oid(rte->coltypes, att->atttypid);
            rte->coltypmods = lappend_int(rte->coltypmods, att->atttypmod);
            rte->colcollations = lappend_oid(rte->colcollations,
                                             att->attcollation);
        }
    }

    /*
     * Set flags and access permissions.
     *
     * ENRs are never checked for access rights.
     */
    rte->lateral = false;
    rte->inh = false;           /* never true for ENRs */
    rte->inFromCl = inFromCl;

    rte->requiredPerms = 0;
    rte->checkAsUser = InvalidOid;
    rte->selectedCols = NULL;

    /*
     * Add completed RTE to pstate's range table list, so that we know its
     * index.  But we don't add it to the join list --- caller must do that if
     * appropriate.
     */
    pstate->p_rtable = lappend(pstate->p_rtable, rte);

    /*
     * Build a ParseNamespaceItem, but don't add it to the pstate's namespace
     * list --- caller must do that if appropriate.
     */
    return buildNSItemFromTupleDesc(rte, list_length(pstate->p_rtable),
                                    tupdesc);
}


/*
 * Has the specified refname been selected FOR UPDATE/FOR SHARE?
 *
 * This is used when we have not yet done transformLockingClause, but need
 * to know the correct lock to take during initial opening of relations.
 *
 * Note: we pay no attention to whether it's FOR UPDATE vs FOR SHARE,
 * since the table-level lock is the same either way.
 */
bool
isLockedRefname(ParseState *pstate, const char *refname)
{
    ListCell   *l;

    /*
     * If we are in a subquery specified as locked FOR UPDATE/SHARE from
     * parent level, then act as though there's a generic FOR UPDATE here.
     */
    if (pstate->p_locked_from_parent)
        return true;

    foreach(l, pstate->p_locking_clause)
    {
        LockingClause *lc = (LockingClause *) lfirst(l);

        if (lc->lockedRels == NIL)
        {
            /* all tables used in query */
            return true;
        }
        else
        {
            /* just the named tables */
            ListCell   *l2;

            foreach(l2, lc->lockedRels)
            {
                RangeVar   *thisrel = (RangeVar *) lfirst(l2);

                if (strcmp(refname, thisrel->relname) == 0)
                    return true;
            }
        }
    }
    return false;
}

/*
 * Add the given nsitem/RTE as a top-level entry in the pstate's join list
 * and/or namespace list.  (We assume caller has checked for any
 * namespace conflicts.)  The nsitem is always marked as unconditionally
 * visible, that is, not LATERAL-only.
 */
void
addNSItemToQuery(ParseState *pstate, ParseNamespaceItem *nsitem,
                 bool addToJoinList,
                 bool addToRelNameSpace, bool addToVarNameSpace)
{
    if (addToJoinList)
    {
        RangeTblRef *rtr = makeNode(RangeTblRef);

        rtr->rtindex = nsitem->p_rtindex;
        pstate->p_joinlist = lappend(pstate->p_joinlist, rtr);
    }
    if (addToRelNameSpace || addToVarNameSpace)
    {
        /* Set the new nsitem's visibility flags correctly */
        nsitem->p_rel_visible = addToRelNameSpace;
        nsitem->p_cols_visible = addToVarNameSpace;
        nsitem->p_lateral_only = false;
        nsitem->p_lateral_ok = true;
        pstate->p_namespace = lappend(pstate->p_namespace, nsitem);
    }
}

/*
 * expandRTE -- expand the columns of a rangetable entry
 *
 * This creates lists of an RTE's column names (aliases if provided, else
 * real names) and Vars for each column.  Only user columns are considered.
 * If include_dropped is false then dropped columns are omitted from the
 * results.  If include_dropped is true then empty strings and NULL constants
 * (not Vars!) are returned for dropped columns.
 *
 * rtindex, sublevels_up, and location are the varno, varlevelsup, and location
 * values to use in the created Vars.  Ordinarily rtindex should match the
 * actual position of the RTE in its rangetable.
 *
 * The output lists go into *colnames and *colvars.
 * If only one of the two kinds of output list is needed, pass NULL for the
 * output pointer for the unwanted one.
 */
void
expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
          int location, bool include_dropped,
          List **colnames, List **colvars)
{
    int         varattno;

    if (colnames)
        *colnames = NIL;
    if (colvars)
        *colvars = NIL;

    switch (rte->rtekind)
    {
        case RTE_RELATION:
            /* Ordinary relation RTE */
            expandRelation(rte->relid, rte->eref,
                           rtindex, sublevels_up, location,
                           include_dropped, colnames, colvars);
            break;
        case RTE_SUBQUERY:
            {
                /* Subquery RTE */
                ListCell   *aliasp_item = list_head(rte->eref->colnames);
                ListCell   *tlistitem;

                varattno = 0;
                foreach(tlistitem, rte->subquery->targetList)
                {
                    TargetEntry *te = (TargetEntry *) lfirst(tlistitem);

                    if (te->resjunk)
                        continue;
                    varattno++;
                    Assert(varattno == te->resno);

                    /*
                     * In scenarios where columns have been added to a view
                     * since the outer query was originally parsed, there can
                     * be more items in the subquery tlist than the outer
                     * query expects.  We should ignore such extra column(s)
                     * --- compare the behavior for composite-returning
                     * functions, in the RTE_FUNCTION case below.
                     */
                    if (!aliasp_item)
                        break;

                    if (colnames)
                    {
                        char       *label = strVal(lfirst(aliasp_item));

                        *colnames = lappend(*colnames, makeString(pstrdup(label)));
                    }

                    if (colvars)
                    {
                        Var        *varnode;

                        varnode = makeVar(rtindex, varattno,
                                          exprType((Node *) te->expr),
                                          exprTypmod((Node *) te->expr),
                                          exprCollation((Node *) te->expr),
                                          sublevels_up);
                        varnode->location = location;

                        *colvars = lappend(*colvars, varnode);
                    }

                    aliasp_item = lnext(rte->eref->colnames, aliasp_item);
                }
            }
            break;
        case RTE_FUNCTION:
            {
                /* Function RTE */
                int         atts_done = 0;
                ListCell   *lc;

                foreach(lc, rte->functions)
                {
                    RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);
                    TypeFuncClass functypclass;
                    Oid         funcrettype;
                    TupleDesc   tupdesc;

                    functypclass = get_expr_result_type(rtfunc->funcexpr,
                                                        &funcrettype,
                                                        &tupdesc);
                    if (functypclass == TYPEFUNC_COMPOSITE ||
                        functypclass == TYPEFUNC_COMPOSITE_DOMAIN)
                    {
                        /* Composite data type, e.g. a table's row type */
                        Assert(tupdesc);
                        expandTupleDesc(tupdesc, rte->eref,
                                        rtfunc->funccolcount, atts_done,
                                        rtindex, sublevels_up, location,
                                        include_dropped, colnames, colvars);
                    }
                    else if (functypclass == TYPEFUNC_SCALAR)
                    {
                        /* Base data type, i.e. scalar */
                        if (colnames)
                            *colnames = lappend(*colnames,
                                                list_nth(rte->eref->colnames,
                                                         atts_done));

                        if (colvars)
                        {
                            Var        *varnode;

                            varnode = makeVar(rtindex, atts_done + 1,
                                              funcrettype,
                                              exprTypmod(rtfunc->funcexpr),
                                              exprCollation(rtfunc->funcexpr),
                                              sublevels_up);
                            varnode->location = location;

                            *colvars = lappend(*colvars, varnode);
                        }
                    }
                    else if (functypclass == TYPEFUNC_RECORD)
                    {
                        if (colnames)
                        {
                            List       *namelist;

                            /* extract appropriate subset of column list */
                            namelist = list_copy_tail(rte->eref->colnames,
                                                      atts_done);
                            namelist = list_truncate(namelist,
                                                     rtfunc->funccolcount);
                            *colnames = list_concat(*colnames, namelist);
                        }

                        if (colvars)
                        {
                            ListCell   *l1;
                            ListCell   *l2;
                            ListCell   *l3;
                            int         attnum = atts_done;

                            forthree(l1, rtfunc->funccoltypes,
                                     l2, rtfunc->funccoltypmods,
                                     l3, rtfunc->funccolcollations)
                            {
                                Oid         attrtype = lfirst_oid(l1);
                                int32       attrtypmod = lfirst_int(l2);
                                Oid         attrcollation = lfirst_oid(l3);
                                Var        *varnode;

                                attnum++;
                                varnode = makeVar(rtindex,
                                                  attnum,
                                                  attrtype,
                                                  attrtypmod,
                                                  attrcollation,
                                                  sublevels_up);
                                varnode->location = location;
                                *colvars = lappend(*colvars, varnode);
                            }
                        }
                    }
                    else
                    {
                        /* addRangeTableEntryForFunction should've caught this */
                        elog(ERROR, "function in FROM has unsupported return type");
                    }
                    atts_done += rtfunc->funccolcount;
                }

                /* Append the ordinality column if any */
                if (rte->funcordinality)
                {
                    if (colnames)
                        *colnames = lappend(*colnames,
                                            llast(rte->eref->colnames));

                    if (colvars)
                    {
                        Var        *varnode = makeVar(rtindex,
                                                      atts_done + 1,
                                                      INT8OID,
                                                      -1,
                                                      InvalidOid,
                                                      sublevels_up);

                        *colvars = lappend(*colvars, varnode);
                    }
                }
            }
            break;
        case RTE_JOIN:
            {
                /* Join RTE */
                ListCell   *colname;
                ListCell   *aliasvar;

                Assert(list_length(rte->eref->colnames) == list_length(rte->joinaliasvars));

                varattno = 0;
                forboth(colname, rte->eref->colnames, aliasvar, rte->joinaliasvars)
                {
                    Node       *avar = (Node *) lfirst(aliasvar);

                    varattno++;

                    /*
                     * During ordinary parsing, there will never be any
                     * deleted columns in the join.  While this function is
                     * also used by the rewriter and planner, they do not
                     * currently call it on any JOIN RTEs.  Therefore, this
                     * next bit is dead code, but it seems prudent to handle
                     * the case correctly anyway.
                     */
                    if (avar == NULL)
                    {
                        if (include_dropped)
                        {
                            if (colnames)
                                *colnames = lappend(*colnames,
                                                    makeString(pstrdup("")));
                            if (colvars)
                            {
                                /*
                                 * Can't use join's column type here (it might
                                 * be dropped!); but it doesn't really matter
                                 * what type the Const claims to be.
                                 */
                                *colvars = lappend(*colvars,
                                                   makeNullConst(INT4OID, -1,
                                                                 InvalidOid));
                            }
                        }
                        continue;
                    }

                    if (colnames)
                    {
                        char       *label = strVal(lfirst(colname));

                        *colnames = lappend(*colnames,
                                            makeString(pstrdup(label)));
                    }

                    if (colvars)
                    {
                        Var        *varnode;

                        /*
                         * If the joinaliasvars entry is a simple Var, just
                         * copy it (with adjustment of varlevelsup and
                         * location); otherwise it is a JOIN USING column and
                         * we must generate a join alias Var.  This matches
                         * the results that expansion of "join.*" by
                         * expandNSItemVars would have produced, if we had
                         * access to the ParseNamespaceItem for the join.
                         */
                        if (IsA(avar, Var))
                        {
                            varnode = copyObject((Var *) avar);
                            varnode->varlevelsup = sublevels_up;
                        }
                        else
                            varnode = makeVar(rtindex, varattno,
                                              exprType(avar),
                                              exprTypmod(avar),
                                              exprCollation(avar),
                                              sublevels_up);
                        varnode->location = location;

                        *colvars = lappend(*colvars, varnode);
                    }
                }
            }
            break;
        case RTE_TABLEFUNC:
        case RTE_VALUES:
        case RTE_CTE:
        case RTE_NAMEDTUPLESTORE:
            {
                /* Tablefunc, Values, CTE, or ENR RTE */
                ListCell   *aliasp_item = list_head(rte->eref->colnames);
                ListCell   *lct;
                ListCell   *lcm;
                ListCell   *lcc;

                varattno = 0;
                forthree(lct, rte->coltypes,
                         lcm, rte->coltypmods,
                         lcc, rte->colcollations)
                {
                    Oid         coltype = lfirst_oid(lct);
                    int32       coltypmod = lfirst_int(lcm);
                    Oid         colcoll = lfirst_oid(lcc);

                    varattno++;

                    if (colnames)
                    {
                        /* Assume there is one alias per output column */
                        if (OidIsValid(coltype))
                        {
                            char       *label = strVal(lfirst(aliasp_item));

                            *colnames = lappend(*colnames,
                                                makeString(pstrdup(label)));
                        }
                        else if (include_dropped)
                            *colnames = lappend(*colnames,
                                                makeString(pstrdup("")));

                        aliasp_item = lnext(rte->eref->colnames, aliasp_item);
                    }

                    if (colvars)
                    {
                        if (OidIsValid(coltype))
                        {
                            Var        *varnode;

                            varnode = makeVar(rtindex, varattno,
                                              coltype, coltypmod, colcoll,
                                              sublevels_up);
                            varnode->location = location;

                            *colvars = lappend(*colvars, varnode);
                        }
                        else if (include_dropped)
                        {
                            /*
                             * It doesn't really matter what type the Const
                             * claims to be.
                             */
                            *colvars = lappend(*colvars,
                                               makeNullConst(INT4OID, -1,
                                                             InvalidOid));
                        }
                    }
                }
            }
            break;
        case RTE_RESULT:
            /* These expose no columns, so nothing to do */
            break;
        default:
            elog(ERROR, "unrecognized RTE kind: %d", (int) rte->rtekind);
    }
}

/*
 * expandRelation -- expandRTE subroutine
 */
static void
expandRelation(Oid relid, Alias *eref, int rtindex, int sublevels_up,
               int location, bool include_dropped,
               List **colnames, List **colvars)
{
    Relation    rel;

    /* Get the tupledesc and turn it over to expandTupleDesc */
    rel = relation_open(relid, AccessShareLock);
    expandTupleDesc(rel->rd_att, eref, rel->rd_att->natts, 0,
                    rtindex, sublevels_up,
                    location, include_dropped,
                    colnames, colvars);
    relation_close(rel, AccessShareLock);
}

/*
 * expandTupleDesc -- expandRTE subroutine
 *
 * Generate names and/or Vars for the first "count" attributes of the tupdesc,
 * and append them to colnames/colvars.  "offset" is added to the varattno
 * that each Var would otherwise have, and we also skip the first "offset"
 * entries in eref->colnames.  (These provisions allow use of this code for
 * an individual composite-returning function in an RTE_FUNCTION RTE.)
 */
static void
expandTupleDesc(TupleDesc tupdesc, Alias *eref, int count, int offset,
                int rtindex, int sublevels_up,
                int location, bool include_dropped,
                List **colnames, List **colvars)
{
    ListCell   *aliascell;
    int         varattno;

    aliascell = (offset < list_length(eref->colnames)) ?
        list_nth_cell(eref->colnames, offset) : NULL;

    Assert(count <= tupdesc->natts);
    for (varattno = 0; varattno < count; varattno++)
    {
        Form_pg_attribute attr = TupleDescAttr(tupdesc, varattno);

        if (attr->attisdropped)
        {
            if (include_dropped)
            {
                if (colnames)
                    *colnames = lappend(*colnames, makeString(pstrdup("")));
                if (colvars)
                {
                    /*
                     * can't use atttypid here, but it doesn't really matter
                     * what type the Const claims to be.
                     */
                    *colvars = lappend(*colvars,
                                       makeNullConst(INT4OID, -1, InvalidOid));
                }
            }
            if (aliascell)
                aliascell = lnext(eref->colnames, aliascell);
            continue;
        }

        if (colnames)
        {
            char       *label;

            if (aliascell)
            {
                label = strVal(lfirst(aliascell));
                aliascell = lnext(eref->colnames, aliascell);
            }
            else
            {
                /* If we run out of aliases, use the underlying name */
                label = NameStr(attr->attname);
            }
            *colnames = lappend(*colnames, makeString(pstrdup(label)));
        }

        if (colvars)
        {
            Var        *varnode;

            varnode = makeVar(rtindex, varattno + offset + 1,
                              attr->atttypid, attr->atttypmod,
                              attr->attcollation,
                              sublevels_up);
            varnode->location = location;

            *colvars = lappend(*colvars, varnode);
        }
    }
}

/*
 * expandNSItemVars
 *    Produce a list of Vars, and optionally a list of column names,
 *    for the non-dropped columns of the nsitem.
 *
 * The emitted Vars are marked with the given sublevels_up and location.
 *
 * If colnames isn't NULL, a list of String items for the columns is stored
 * there; note that it's just a subset of the RTE's eref list, and hence
 * the list elements mustn't be modified.
 */
List *
expandNSItemVars(ParseNamespaceItem *nsitem,
                 int sublevels_up, int location,
                 List **colnames)
{
    List       *result = NIL;
    int         colindex;
    ListCell   *lc;

    if (colnames)
        *colnames = NIL;
    colindex = 0;
    foreach(lc, nsitem->p_rte->eref->colnames)
    {
        Value      *colnameval = (Value *) lfirst(lc);
        const char *colname = strVal(colnameval);
        ParseNamespaceColumn *nscol = nsitem->p_nscolumns + colindex;

        if (colname[0])
        {
            Var        *var;

            Assert(nscol->p_varno > 0);
            var = makeVar(nscol->p_varno,
                          nscol->p_varattno,
                          nscol->p_vartype,
                          nscol->p_vartypmod,
                          nscol->p_varcollid,
                          sublevels_up);
            /* makeVar doesn't offer parameters for these, so set by hand: */
            var->varnosyn = nscol->p_varnosyn;
            var->varattnosyn = nscol->p_varattnosyn;
            var->location = location;
            result = lappend(result, var);
            if (colnames)
                *colnames = lappend(*colnames, colnameval);
        }
        else
        {
            /* dropped column, ignore */
            Assert(nscol->p_varno == 0);
        }
        colindex++;
    }
    return result;
}

/*
 * expandNSItemAttrs -
 *    Workhorse for "*" expansion: produce a list of targetentries
 *    for the attributes of the nsitem
 *
 * pstate->p_next_resno determines the resnos assigned to the TLEs.
 * The referenced columns are marked as requiring SELECT access.
 */
List *
expandNSItemAttrs(ParseState *pstate, ParseNamespaceItem *nsitem,
                  int sublevels_up, int location)
{
    RangeTblEntry *rte = nsitem->p_rte;
    List       *names,
               *vars;
    ListCell   *name,
               *var;
    List       *te_list = NIL;

    vars = expandNSItemVars(nsitem, sublevels_up, location, &names);

    /*
     * Require read access to the table.  This is normally redundant with the
     * markVarForSelectPriv calls below, but not if the table has zero
     * columns.
     */
    rte->requiredPerms |= ACL_SELECT;

    forboth(name, names, var, vars)
    {
        char       *label = strVal(lfirst(name));
        Var        *varnode = (Var *) lfirst(var);
        TargetEntry *te;

        te = makeTargetEntry((Expr *) varnode,
                             (AttrNumber) pstate->p_next_resno++,
                             label,
                             false);
        te_list = lappend(te_list, te);

        /* Require read access to each column */
        markVarForSelectPriv(pstate, varnode, rte);
    }

    Assert(name == NULL && var == NULL);    /* lists not the same length? */

    return te_list;
}

/*
 * get_rte_attribute_name
 *      Get an attribute name from a RangeTblEntry
 *
 * This is unlike get_attname() because we use aliases if available.
 * In particular, it will work on an RTE for a subselect or join, whereas
 * get_attname() only works on real relations.
 *
 * "*" is returned if the given attnum is InvalidAttrNumber --- this case
 * occurs when a Var represents a whole tuple of a relation.
 */
char *
get_rte_attribute_name(RangeTblEntry *rte, AttrNumber attnum)
{
    if (attnum == InvalidAttrNumber)
        return "*";

    /*
     * If there is a user-written column alias, use it.
     */
    if (rte->alias &&
        attnum > 0 && attnum <= list_length(rte->alias->colnames))
        return strVal(list_nth(rte->alias->colnames, attnum - 1));

    /*
     * If the RTE is a relation, go to the system catalogs not the
     * eref->colnames list.  This is a little slower but it will give the
     * right answer if the column has been renamed since the eref list was
     * built (which can easily happen for rules).
     */
    if (rte->rtekind == RTE_RELATION)
        return get_attname(rte->relid, attnum, false);

    /*
     * Otherwise use the column name from eref.  There should always be one.
     */
    if (attnum > 0 && attnum <= list_length(rte->eref->colnames))
        return strVal(list_nth(rte->eref->colnames, attnum - 1));

    /* else caller gave us a bogus attnum */
    elog(ERROR, "invalid attnum %d for rangetable entry %s",
         attnum, rte->eref->aliasname);
    return NULL;                /* keep compiler quiet */
}

/*
 * get_rte_attribute_is_dropped
 *      Check whether attempted attribute ref is to a dropped column
 */
bool
get_rte_attribute_is_dropped(RangeTblEntry *rte, AttrNumber attnum)
{
    bool        result;

    switch (rte->rtekind)
    {
        case RTE_RELATION:
            {
                /*
                 * Plain relation RTE --- get the attribute's catalog entry
                 */
                HeapTuple   tp;
                Form_pg_attribute att_tup;

                tp = SearchSysCache2(ATTNUM,
                                     ObjectIdGetDatum(rte->relid),
                                     Int16GetDatum(attnum));
                if (!HeapTupleIsValid(tp))  /* shouldn't happen */
                    elog(ERROR, "cache lookup failed for attribute %d of relation %u",
                         attnum, rte->relid);
                att_tup = (Form_pg_attribute) GETSTRUCT(tp);
                result = att_tup->attisdropped;
                ReleaseSysCache(tp);
            }
            break;
        case RTE_SUBQUERY:
        case RTE_TABLEFUNC:
        case RTE_VALUES:
        case RTE_CTE:

            /*
             * Subselect, Table Functions, Values, CTE RTEs never have dropped
             * columns
             */
            result = false;
            break;
        case RTE_NAMEDTUPLESTORE:
            {
                /* Check dropped-ness by testing for valid coltype */
                if (attnum <= 0 ||
                    attnum > list_length(rte->coltypes))
                    elog(ERROR, "invalid varattno %d", attnum);
                result = !OidIsValid((list_nth_oid(rte->coltypes, attnum - 1)));
            }
            break;
        case RTE_JOIN:
            {
                /*
                 * A join RTE would not have dropped columns when constructed,
                 * but one in a stored rule might contain columns that were
                 * dropped from the underlying tables, if said columns are
                 * nowhere explicitly referenced in the rule.  This will be
                 * signaled to us by a null pointer in the joinaliasvars list.
                 */
                Var        *aliasvar;

                if (attnum <= 0 ||
                    attnum > list_length(rte->joinaliasvars))
                    elog(ERROR, "invalid varattno %d", attnum);
                aliasvar = (Var *) list_nth(rte->joinaliasvars, attnum - 1);

                result = (aliasvar == NULL);
            }
            break;
        case RTE_FUNCTION:
            {
                /* Function RTE */
                ListCell   *lc;
                int         atts_done = 0;

                /*
                 * Dropped attributes are only possible with functions that
                 * return named composite types.  In such a case we have to
                 * look up the result type to see if it currently has this
                 * column dropped.  So first, loop over the funcs until we
                 * find the one that covers the requested column.
                 */
                foreach(lc, rte->functions)
                {
                    RangeTblFunction *rtfunc = (RangeTblFunction *) lfirst(lc);

                    if (attnum > atts_done &&
                        attnum <= atts_done + rtfunc->funccolcount)
                    {
                        TupleDesc   tupdesc;

                        tupdesc = get_expr_result_tupdesc(rtfunc->funcexpr,
                                                          true);
                        if (tupdesc)
                        {
                            /* Composite data type, e.g. a table's row type */
                            Form_pg_attribute att_tup;

                            Assert(tupdesc);
                            Assert(attnum - atts_done <= tupdesc->natts);
                            att_tup = TupleDescAttr(tupdesc,
                                                    attnum - atts_done - 1);
                            return att_tup->attisdropped;
                        }
                        /* Otherwise, it can't have any dropped columns */
                        return false;
                    }
                    atts_done += rtfunc->funccolcount;
                }

                /* If we get here, must be looking for the ordinality column */
                if (rte->funcordinality && attnum == atts_done + 1)
                    return false;

                /* this probably can't happen ... */
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_COLUMN),
                         errmsg("column %d of relation \"%s\" does not exist",
                                attnum,
                                rte->eref->aliasname)));
                result = false; /* keep compiler quiet */
            }
            break;
        case RTE_RESULT:
            /* this probably can't happen ... */
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_COLUMN),
                     errmsg("column %d of relation \"%s\" does not exist",
                            attnum,
                            rte->eref->aliasname)));
            result = false;     /* keep compiler quiet */
            break;
        default:
            elog(ERROR, "unrecognized RTE kind: %d", (int) rte->rtekind);
            result = false;     /* keep compiler quiet */
    }

    return result;
}

/*
 * Given a targetlist and a resno, return the matching TargetEntry
 *
 * Returns NULL if resno is not present in list.
 *
 * Note: we need to search, rather than just indexing with list_nth(),
 * because not all tlists are sorted by resno.
 */
TargetEntry *
get_tle_by_resno(List *tlist, AttrNumber resno)
{
    ListCell   *l;

    foreach(l, tlist)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(l);

        if (tle->resno == resno)
            return tle;
    }
    return NULL;
}

/*
 * Given a Query and rangetable index, return relation's RowMarkClause if any
 *
 * Returns NULL if relation is not selected FOR UPDATE/SHARE
 */
RowMarkClause *
get_parse_rowmark(Query *qry, Index rtindex)
{
    ListCell   *l;

    foreach(l, qry->rowMarks)
    {
        RowMarkClause *rc = (RowMarkClause *) lfirst(l);

        if (rc->rti == rtindex)
            return rc;
    }
    return NULL;
}

/*
 *  given relation and att name, return attnum of variable
 *
 *  Returns InvalidAttrNumber if the attr doesn't exist (or is dropped).
 *
 *  This should only be used if the relation is already
 *  table_open()'ed.  Use the cache version get_attnum()
 *  for access to non-opened relations.
 */
int
attnameAttNum(Relation rd, const char *attname, bool sysColOK)
{
    int         i;

    for (i = 0; i < RelationGetNumberOfAttributes(rd); i++)
    {
        Form_pg_attribute att = TupleDescAttr(rd->rd_att, i);

        if (namestrcmp(&(att->attname), attname) == 0 && !att->attisdropped)
            return i + 1;
    }

    if (sysColOK)
    {
        if ((i = specialAttNum(attname)) != InvalidAttrNumber)
            return i;
    }

    /* on failure */
    return InvalidAttrNumber;
}

/* specialAttNum()
 *
 * Check attribute name to see if it is "special", e.g. "xmin".
 * - thomas 2000-02-07
 *
 * Note: this only discovers whether the name could be a system attribute.
 * Caller needs to ensure that it really is an attribute of the rel.
 */
static int
specialAttNum(const char *attname)
{
    const FormData_pg_attribute *sysatt;

    sysatt = SystemAttributeByName(attname);
    if (sysatt != NULL)
        return sysatt->attnum;
    return InvalidAttrNumber;
}


/*
 * given attribute id, return name of that attribute
 *
 *  This should only be used if the relation is already
 *  table_open()'ed.  Use the cache version get_atttype()
 *  for access to non-opened relations.
 */
const NameData *
attnumAttName(Relation rd, int attid)
{
    if (attid <= 0)
    {
        const FormData_pg_attribute *sysatt;

        sysatt = SystemAttributeDefinition(attid);
        return &sysatt->attname;
    }
    if (attid > rd->rd_att->natts)
        elog(ERROR, "invalid attribute number %d", attid);
    return &TupleDescAttr(rd->rd_att, attid - 1)->attname;
}

/*
 * given attribute id, return type of that attribute
 *
 *  This should only be used if the relation is already
 *  table_open()'ed.  Use the cache version get_atttype()
 *  for access to non-opened relations.
 */
Oid
attnumTypeId(Relation rd, int attid)
{
    if (attid <= 0)
    {
        const FormData_pg_attribute *sysatt;

        sysatt = SystemAttributeDefinition(attid);
        return sysatt->atttypid;
    }
    if (attid > rd->rd_att->natts)
        elog(ERROR, "invalid attribute number %d", attid);
    return TupleDescAttr(rd->rd_att, attid - 1)->atttypid;
}

/*
 * given attribute id, return collation of that attribute
 *
 *  This should only be used if the relation is already table_open()'ed.
 */
Oid
attnumCollationId(Relation rd, int attid)
{
    if (attid <= 0)
    {
        /* All system attributes are of noncollatable types. */
        return InvalidOid;
    }
    if (attid > rd->rd_att->natts)
        elog(ERROR, "invalid attribute number %d", attid);
    return TupleDescAttr(rd->rd_att, attid - 1)->attcollation;
}

/*
 * Generate a suitable error about a missing RTE.
 *
 * Since this is a very common type of error, we work rather hard to
 * produce a helpful message.
 */
void
errorMissingRTE(ParseState *pstate, RangeVar *relation)
{
    RangeTblEntry *rte;
    const char *badAlias = NULL;

    /*
     * Check to see if there are any potential matches in the query's
     * rangetable.  (Note: cases involving a bad schema name in the RangeVar
     * will throw error immediately here.  That seems OK.)
     */
    rte = searchRangeTableForRel(pstate, relation);

    /*
     * If we found a match that has an alias and the alias is visible in the
     * namespace, then the problem is probably use of the relation's real name
     * instead of its alias, ie "SELECT foo.* FROM foo f". This mistake is
     * common enough to justify a specific hint.
     *
     * If we found a match that doesn't meet those criteria, assume the
     * problem is illegal use of a relation outside its scope, as in the
     * MySQL-ism "SELECT ... FROM a, b LEFT JOIN c ON (a.x = c.y)".
     */
    if (rte && rte->alias &&
        strcmp(rte->eref->aliasname, relation->relname) != 0)
    {
        ParseNamespaceItem *nsitem;
        int         sublevels_up;

        nsitem = refnameNamespaceItem(pstate, NULL, rte->eref->aliasname,
                                      relation->location,
                                      &sublevels_up);
        if (nsitem && nsitem->p_rte == rte)
            badAlias = rte->eref->aliasname;
    }

    if (rte)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_TABLE),
                 errmsg("invalid reference to FROM-clause entry for table \"%s\"",
                        relation->relname),
                 (badAlias ?
                  errhint("Perhaps you meant to reference the table alias \"%s\".",
                          badAlias) :
                  errhint("There is an entry for table \"%s\", but it cannot be referenced from this part of the query.",
                          rte->eref->aliasname)),
                 parser_errposition(pstate, relation->location)));
    else
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_TABLE),
                 errmsg("missing FROM-clause entry for table \"%s\"",
                        relation->relname),
                 parser_errposition(pstate, relation->location)));
}

/*
 * Generate a suitable error about a missing column.
 *
 * Since this is a very common type of error, we work rather hard to
 * produce a helpful message.
 */
void
errorMissingColumn(ParseState *pstate,
                   const char *relname, const char *colname, int location)
{
    FuzzyAttrMatchState *state;
    char       *closestfirst = NULL;

    /*
     * Search the entire rtable looking for possible matches.  If we find one,
     * emit a hint about it.
     *
     * TODO: improve this code (and also errorMissingRTE) to mention using
     * LATERAL if appropriate.
     */
    state = searchRangeTableForCol(pstate, relname, colname, location);

    /*
     * Extract closest col string for best match, if any.
     *
     * Infer an exact match referenced despite not being visible from the fact
     * that an attribute number was not present in state passed back -- this
     * is what is reported when !closestfirst.  There might also be an exact
     * match that was qualified with an incorrect alias, in which case
     * closestfirst will be set (so hint is the same as generic fuzzy case).
     */
    if (state->rfirst && AttributeNumberIsValid(state->first))
        closestfirst = strVal(list_nth(state->rfirst->eref->colnames,
                                       state->first - 1));

    if (!state->rsecond)
    {
        /*
         * Handle case where there is zero or one column suggestions to hint,
         * including exact matches referenced but not visible.
         */
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 relname ?
                 errmsg("column %s.%s does not exist", relname, colname) :
                 errmsg("column \"%s\" does not exist", colname),
                 state->rfirst ? closestfirst ?
                 errhint("Perhaps you meant to reference the column \"%s.%s\".",
                         state->rfirst->eref->aliasname, closestfirst) :
                 errhint("There is a column named \"%s\" in table \"%s\", but it cannot be referenced from this part of the query.",
                         colname, state->rfirst->eref->aliasname) : 0,
                 parser_errposition(pstate, location)));
    }
    else
    {
        /* Handle case where there are two equally useful column hints */
        char       *closestsecond;

        closestsecond = strVal(list_nth(state->rsecond->eref->colnames,
                                        state->second - 1));

        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 relname ?
                 errmsg("column %s.%s does not exist", relname, colname) :
                 errmsg("column \"%s\" does not exist", colname),
                 errhint("Perhaps you meant to reference the column \"%s.%s\" or the column \"%s.%s\".",
                         state->rfirst->eref->aliasname, closestfirst,
                         state->rsecond->eref->aliasname, closestsecond),
                 parser_errposition(pstate, location)));
    }
}


/*
 * Examine a fully-parsed query, and return true iff any relation underlying
 * the query is a temporary relation (table, view, or materialized view).
 */
bool
isQueryUsingTempRelation(Query *query)
{
    return isQueryUsingTempRelation_walker((Node *) query, NULL);
}

static bool
isQueryUsingTempRelation_walker(Node *node, void *context)
{
    if (node == NULL)
        return false;

    if (IsA(node, Query))
    {
        Query      *query = (Query *) node;
        ListCell   *rtable;

        foreach(rtable, query->rtable)
        {
            RangeTblEntry *rte = lfirst(rtable);

            if (rte->rtekind == RTE_RELATION)
            {
                Relation    rel = table_open(rte->relid, AccessShareLock);
                char        relpersistence = rel->rd_rel->relpersistence;

                table_close(rel, AccessShareLock);
                if (relpersistence == RELPERSISTENCE_TEMP)
                    return true;
            }
        }

        return query_tree_walker(query,
                                 isQueryUsingTempRelation_walker,
                                 context,
                                 QTW_IGNORE_JOINALIASES);
    }

    return expression_tree_walker(node,
                                  isQueryUsingTempRelation_walker,
                                  context);
}