/*-------------------------------------------------------------------------

 *

 * 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);

}