view.c

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/*-------------------------------------------------------------------------
 *
 * view.c
 *    use rewrite rules to construct views
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/view.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/relation.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "commands/defrem.h"
#include "commands/tablecmds.h"
#include "commands/view.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/analyze.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rewriteSupport.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"

static void checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc);

/*---------------------------------------------------------------------
 * DefineVirtualRelation
 *
 * Create a view relation and use the rules system to store the query
 * for the view.
 *
 * EventTriggerAlterTableStart must have been called already.
 *---------------------------------------------------------------------
 */
static ObjectAddress
DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
                      List *options, Query *viewParse)
{
    Oid         viewOid;
    LOCKMODE    lockmode;
    CreateStmt *createStmt = makeNode(CreateStmt);
    List       *attrList;
    ListCell   *t;

    /*
     * create a list of ColumnDef nodes based on the names and types of the
     * (non-junk) targetlist items from the view's SELECT list.
     */
    attrList = NIL;
    foreach(t, tlist)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(t);

        if (!tle->resjunk)
        {
            ColumnDef  *def = makeColumnDef(tle->resname,
                                            exprType((Node *) tle->expr),
                                            exprTypmod((Node *) tle->expr),
                                            exprCollation((Node *) tle->expr));

            /*
             * It's possible that the column is of a collatable type but the
             * collation could not be resolved, so double-check.
             */
            if (type_is_collatable(exprType((Node *) tle->expr)))
            {
                if (!OidIsValid(def->collOid))
                    ereport(ERROR,
                            (errcode(ERRCODE_INDETERMINATE_COLLATION),
                             errmsg("could not determine which collation to use for view column \"%s\"",
                                    def->colname),
                             errhint("Use the COLLATE clause to set the collation explicitly.")));
            }
            else
                Assert(!OidIsValid(def->collOid));

            attrList = lappend(attrList, def);
        }
    }

    /*
     * Look up, check permissions on, and lock the creation namespace; also
     * check for a preexisting view with the same name.  This will also set
     * relation->relpersistence to RELPERSISTENCE_TEMP if the selected
     * namespace is temporary.
     */
    lockmode = replace ? AccessExclusiveLock : NoLock;
    (void) RangeVarGetAndCheckCreationNamespace(relation, lockmode, &viewOid);

    if (OidIsValid(viewOid) && replace)
    {
        Relation    rel;
        TupleDesc   descriptor;
        List       *atcmds = NIL;
        AlterTableCmd *atcmd;
        ObjectAddress address;

        /* Relation is already locked, but we must build a relcache entry. */
        rel = relation_open(viewOid, NoLock);

        /* Make sure it *is* a view. */
        if (rel->rd_rel->relkind != RELKIND_VIEW)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("\"%s\" is not a view",
                            RelationGetRelationName(rel))));

        /* Also check it's not in use already */
        CheckTableNotInUse(rel, "CREATE OR REPLACE VIEW");

        /*
         * Due to the namespace visibility rules for temporary objects, we
         * should only end up replacing a temporary view with another
         * temporary view, and similarly for permanent views.
         */
        Assert(relation->relpersistence == rel->rd_rel->relpersistence);

        /*
         * Create a tuple descriptor to compare against the existing view, and
         * verify that the old column list is an initial prefix of the new
         * column list.
         */
        descriptor = BuildDescForRelation(attrList);
        checkViewTupleDesc(descriptor, rel->rd_att);

        /*
         * If new attributes have been added, we must add pg_attribute entries
         * for them.  It is convenient (although overkill) to use the ALTER
         * TABLE ADD COLUMN infrastructure for this.
         *
         * Note that we must do this before updating the query for the view,
         * since the rules system requires that the correct view columns be in
         * place when defining the new rules.
         *
         * Also note that ALTER TABLE doesn't run parse transformation on
         * AT_AddColumnToView commands.  The ColumnDef we supply must be ready
         * to execute as-is.
         */
        if (list_length(attrList) > rel->rd_att->natts)
        {
            ListCell   *c;
            int         skip = rel->rd_att->natts;

            foreach(c, attrList)
            {
                if (skip > 0)
                {
                    skip--;
                    continue;
                }
                atcmd = makeNode(AlterTableCmd);
                atcmd->subtype = AT_AddColumnToView;
                atcmd->def = (Node *) lfirst(c);
                atcmds = lappend(atcmds, atcmd);
            }

            /* EventTriggerAlterTableStart called by ProcessUtilitySlow */
            AlterTableInternal(viewOid, atcmds, true);

            /* Make the new view columns visible */
            CommandCounterIncrement();
        }

        /*
         * Update the query for the view.
         *
         * Note that we must do this before updating the view options, because
         * the new options may not be compatible with the old view query (for
         * example if we attempt to add the WITH CHECK OPTION, we require that
         * the new view be automatically updatable, but the old view may not
         * have been).
         */
        StoreViewQuery(viewOid, viewParse, replace);

        /* Make the new view query visible */
        CommandCounterIncrement();

        /*
         * Finally update the view options.
         *
         * The new options list replaces the existing options list, even if
         * it's empty.
         */
        atcmd = makeNode(AlterTableCmd);
        atcmd->subtype = AT_ReplaceRelOptions;
        atcmd->def = (Node *) options;
        atcmds = list_make1(atcmd);

        /* EventTriggerAlterTableStart called by ProcessUtilitySlow */
        AlterTableInternal(viewOid, atcmds, true);

        ObjectAddressSet(address, RelationRelationId, viewOid);

        /*
         * Seems okay, so return the OID of the pre-existing view.
         */
        relation_close(rel, NoLock);    /* keep the lock! */

        return address;
    }
    else
    {
        ObjectAddress address;

        /*
         * Set the parameters for keys/inheritance etc. All of these are
         * uninteresting for views...
         */
        createStmt->relation = relation;
        createStmt->tableElts = attrList;
        createStmt->inhRelations = NIL;
        createStmt->constraints = NIL;
        createStmt->options = options;
        createStmt->oncommit = ONCOMMIT_NOOP;
        createStmt->tablespacename = NULL;
        createStmt->if_not_exists = false;

        /*
         * Create the relation (this will error out if there's an existing
         * view, so we don't need more code to complain if "replace" is
         * false).
         */
        address = DefineRelation(createStmt, RELKIND_VIEW, InvalidOid, NULL,
                                 NULL);
        Assert(address.objectId != InvalidOid);

        /* Make the new view relation visible */
        CommandCounterIncrement();

        /* Store the query for the view */
        StoreViewQuery(address.objectId, viewParse, replace);

        return address;
    }
}

/*
 * Verify that tupledesc associated with proposed new view definition
 * matches tupledesc of old view.  This is basically a cut-down version
 * of equalTupleDescs(), with code added to generate specific complaints.
 * Also, we allow the new tupledesc to have more columns than the old.
 */
static void
checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
{
    int         i;

    if (newdesc->natts < olddesc->natts)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("cannot drop columns from view")));

    for (i = 0; i < olddesc->natts; i++)
    {
        Form_pg_attribute newattr = TupleDescAttr(newdesc, i);
        Form_pg_attribute oldattr = TupleDescAttr(olddesc, i);

        /* XXX msg not right, but we don't support DROP COL on view anyway */
        if (newattr->attisdropped != oldattr->attisdropped)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot drop columns from view")));

        if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot change name of view column \"%s\" to \"%s\"",
                            NameStr(oldattr->attname),
                            NameStr(newattr->attname)),
                     errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
        /* XXX would it be safe to allow atttypmod to change?  Not sure */
        if (newattr->atttypid != oldattr->atttypid ||
            newattr->atttypmod != oldattr->atttypmod)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot change data type of view column \"%s\" from %s to %s",
                            NameStr(oldattr->attname),
                            format_type_with_typemod(oldattr->atttypid,
                                                     oldattr->atttypmod),
                            format_type_with_typemod(newattr->atttypid,
                                                     newattr->atttypmod))));
        /* We can ignore the remaining attributes of an attribute... */
    }

    /*
     * We ignore the constraint fields.  The new view desc can't have any
     * constraints, and the only ones that could be on the old view are
     * defaults, which we are happy to leave in place.
     */
}

static void
DefineViewRules(Oid viewOid, Query *viewParse, bool replace)
{
    /*
     * Set up the ON SELECT rule.  Since the query has already been through
     * parse analysis, we use DefineQueryRewrite() directly.
     */
    DefineQueryRewrite(pstrdup(ViewSelectRuleName),
                       viewOid,
                       NULL,
                       CMD_SELECT,
                       true,
                       replace,
                       list_make1(viewParse));

    /*
     * Someday: automatic ON INSERT, etc
     */
}

/*---------------------------------------------------------------
 * UpdateRangeTableOfViewParse
 *
 * Update the range table of the given parsetree.
 * This update consists of adding two new entries IN THE BEGINNING
 * of the range table (otherwise the rule system will die a slow,
 * horrible and painful death, and we do not want that now, do we?)
 * one for the OLD relation and one for the NEW one (both of
 * them refer in fact to the "view" relation).
 *
 * Of course we must also increase the 'varnos' of all the Var nodes
 * by 2...
 *
 * These extra RT entries are not actually used in the query,
 * except for run-time locking and permission checking.
 *---------------------------------------------------------------
 */
static Query *
UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
{
    Relation    viewRel;
    List       *new_rt;
    ParseNamespaceItem *nsitem;
    RangeTblEntry *rt_entry1,
               *rt_entry2;
    ParseState *pstate;

    /*
     * Make a copy of the given parsetree.  It's not so much that we don't
     * want to scribble on our input, it's that the parser has a bad habit of
     * outputting multiple links to the same subtree for constructs like
     * BETWEEN, and we mustn't have OffsetVarNodes increment the varno of a
     * Var node twice.  copyObject will expand any multiply-referenced subtree
     * into multiple copies.
     */
    viewParse = copyObject(viewParse);

    /* Create a dummy ParseState for addRangeTableEntryForRelation */
    pstate = make_parsestate(NULL);

    /* need to open the rel for addRangeTableEntryForRelation */
    viewRel = relation_open(viewOid, AccessShareLock);

    /*
     * Create the 2 new range table entries and form the new range table...
     * OLD first, then NEW....
     */
    nsitem = addRangeTableEntryForRelation(pstate, viewRel,
                                           AccessShareLock,
                                           makeAlias("old", NIL),
                                           false, false);
    rt_entry1 = nsitem->p_rte;
    nsitem = addRangeTableEntryForRelation(pstate, viewRel,
                                           AccessShareLock,
                                           makeAlias("new", NIL),
                                           false, false);
    rt_entry2 = nsitem->p_rte;

    /* Must override addRangeTableEntry's default access-check flags */
    rt_entry1->requiredPerms = 0;
    rt_entry2->requiredPerms = 0;

    new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));

    viewParse->rtable = new_rt;

    /*
     * Now offset all var nodes by 2, and jointree RT indexes too.
     */
    OffsetVarNodes((Node *) viewParse, 2, 0);

    relation_close(viewRel, AccessShareLock);

    return viewParse;
}

/*
 * DefineView
 *      Execute a CREATE VIEW command.
 */
ObjectAddress
DefineView(ViewStmt *stmt, const char *queryString,
           int stmt_location, int stmt_len)
{
    RawStmt    *rawstmt;
    Query      *viewParse;
    RangeVar   *view;
    ListCell   *cell;
    bool        check_option;
    ObjectAddress address;

    /*
     * Run parse analysis to convert the raw parse tree to a Query.  Note this
     * also acquires sufficient locks on the source table(s).
     *
     * Since parse analysis scribbles on its input, copy the raw parse tree;
     * this ensures we don't corrupt a prepared statement, for example.
     */
    rawstmt = makeNode(RawStmt);
    rawstmt->stmt = (Node *) copyObject(stmt->query);
    rawstmt->stmt_location = stmt_location;
    rawstmt->stmt_len = stmt_len;

    viewParse = parse_analyze(rawstmt, queryString, NULL, 0, NULL);

    /*
     * The grammar should ensure that the result is a single SELECT Query.
     * However, it doesn't forbid SELECT INTO, so we have to check for that.
     */
    if (!IsA(viewParse, Query))
        elog(ERROR, "unexpected parse analysis result");
    if (viewParse->utilityStmt != NULL &&
        IsA(viewParse->utilityStmt, CreateTableAsStmt))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("views must not contain SELECT INTO")));
    if (viewParse->commandType != CMD_SELECT)
        elog(ERROR, "unexpected parse analysis result");

    /*
     * Check for unsupported cases.  These tests are redundant with ones in
     * DefineQueryRewrite(), but that function will complain about a bogus ON
     * SELECT rule, and we'd rather the message complain about a view.
     */
    if (viewParse->hasModifyingCTE)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("views must not contain data-modifying statements in WITH")));

    /*
     * If the user specified the WITH CHECK OPTION, add it to the list of
     * reloptions.
     */
    if (stmt->withCheckOption == LOCAL_CHECK_OPTION)
        stmt->options = lappend(stmt->options,
                                makeDefElem("check_option",
                                            (Node *) makeString("local"), -1));
    else if (stmt->withCheckOption == CASCADED_CHECK_OPTION)
        stmt->options = lappend(stmt->options,
                                makeDefElem("check_option",
                                            (Node *) makeString("cascaded"), -1));

    /*
     * Check that the view is auto-updatable if WITH CHECK OPTION was
     * specified.
     */
    check_option = false;

    foreach(cell, stmt->options)
    {
        DefElem    *defel = (DefElem *) lfirst(cell);

        if (strcmp(defel->defname, "check_option") == 0)
            check_option = true;
    }

    /*
     * If the check option is specified, look to see if the view is actually
     * auto-updatable or not.
     */
    if (check_option)
    {
        const char *view_updatable_error =
        view_query_is_auto_updatable(viewParse, true);

        if (view_updatable_error)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("WITH CHECK OPTION is supported only on automatically updatable views"),
                     errhint("%s", _(view_updatable_error))));
    }

    /*
     * If a list of column names was given, run through and insert these into
     * the actual query tree. - thomas 2000-03-08
     */
    if (stmt->aliases != NIL)
    {
        ListCell   *alist_item = list_head(stmt->aliases);
        ListCell   *targetList;

        foreach(targetList, viewParse->targetList)
        {
            TargetEntry *te = lfirst_node(TargetEntry, targetList);

            /* junk columns don't get aliases */
            if (te->resjunk)
                continue;
            te->resname = pstrdup(strVal(lfirst(alist_item)));
            alist_item = lnext(stmt->aliases, alist_item);
            if (alist_item == NULL)
                break;          /* done assigning aliases */
        }

        if (alist_item != NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("CREATE VIEW specifies more column "
                            "names than columns")));
    }

    /* Unlogged views are not sensible. */
    if (stmt->view->relpersistence == RELPERSISTENCE_UNLOGGED)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("views cannot be unlogged because they do not have storage")));

    /*
     * If the user didn't explicitly ask for a temporary view, check whether
     * we need one implicitly.  We allow TEMP to be inserted automatically as
     * long as the CREATE command is consistent with that --- no explicit
     * schema name.
     */
    view = copyObject(stmt->view);  /* don't corrupt original command */
    if (view->relpersistence == RELPERSISTENCE_PERMANENT
        && isQueryUsingTempRelation(viewParse))
    {
        view->relpersistence = RELPERSISTENCE_TEMP;
        ereport(NOTICE,
                (errmsg("view \"%s\" will be a temporary view",
                        view->relname)));
    }

    /*
     * Create the view relation
     *
     * NOTE: if it already exists and replace is false, the xact will be
     * aborted.
     */
    address = DefineVirtualRelation(view, viewParse->targetList,
                                    stmt->replace, stmt->options, viewParse);

    return address;
}

/*
 * Use the rules system to store the query for the view.
 */
void
StoreViewQuery(Oid viewOid, Query *viewParse, bool replace)
{
    /*
     * The range table of 'viewParse' does not contain entries for the "OLD"
     * and "NEW" relations. So... add them!
     */
    viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);

    /*
     * Now create the rules associated with the view.
     */
    DefineViewRules(viewOid, viewParse, replace);
}