view.c

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/*-------------------------------------------------------------------------
 *
 * view.c
 *    use rewrite rules to construct views
 *
 * Portions Copyright (c) 1996-2025, 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/tablecmds.h"
#include "commands/view.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/rewriteSupport.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
 
static void checkViewColumns(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;
    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);
        checkViewColumns(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();
 
        /*
         * Update the view's 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);
 
        /*
         * There is very little to do here to update the view's dependencies.
         * Most view-level dependency relationships, such as those on the
         * owner, schema, and associated composite type, aren't changing.
         * Because we don't allow changing type or collation of an existing
         * view column, those dependencies of the existing columns don't
         * change either, while the AT_AddColumnToView machinery took care of
         * adding such dependencies for new view columns.  The dependencies of
         * the view's query could have changed arbitrarily, but that was dealt
         * with inside StoreViewQuery.  What remains is only to check that
         * view replacement is allowed when we're creating an extension.
         */
        ObjectAddressSet(address, RelationRelationId, viewOid);
 
        recordDependencyOnCurrentExtension(&address, true);
 
        /*
         * Seems okay, so return the OID of the pre-existing view.
         */
        relation_close(rel, NoLock);    /* keep the lock! */
 
        return address;
    }
    else
    {
        CreateStmt *createStmt = makeNode(CreateStmt);
        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 the columns associated with proposed new view definition match
 * the columns of the old view.  This is similar to equalRowTypes(), with code
 * added to generate specific complaints.  Also, we allow the new view to have
 * more columns than the old.
 */
static void
checkViewColumns(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.")));
 
        /*
         * We cannot allow type, typmod, or collation to change, since these
         * properties may be embedded in Vars of other views/rules referencing
         * this one.  Other column attributes can be ignored.
         */
        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))));
 
        /*
         * At this point, attcollations should be both valid or both invalid,
         * so applying get_collation_name unconditionally should be fine.
         */
        if (newattr->attcollation != oldattr->attcollation)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
                            NameStr(oldattr->attname),
                            get_collation_name(oldattr->attcollation),
                            get_collation_name(newattr->attcollation))));
    }
 
    /*
     * 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
     */
}
 
/*
 * 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).
     */
    rawstmt = makeNode(RawStmt);
    rawstmt->stmt = stmt->query;
    rawstmt->stmt_location = stmt_location;
    rawstmt->stmt_len = stmt_len;
 
    viewParse = parse_analyze_fixedparams(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)
{
    /*
     * Now create the rules associated with the view.
     */
    DefineViewRules(viewOid, viewParse, replace);
}