path: root/src/backend/optimizer/prep/preptlist.c

/*-------------------------------------------------------------------------
 *
 * preptlist.c
 *	  Routines to preprocess the parse tree target list
 *
 * For an INSERT, the targetlist must contain an entry for each attribute of
 * the target relation in the correct order.
 *
 * For an UPDATE, the targetlist just contains the expressions for the new
 * column values.
 *
 * For UPDATE and DELETE queries, the targetlist must also contain "junk"
 * tlist entries needed to allow the executor to identify the rows to be
 * updated or deleted; for example, the ctid of a heap row.  (The planner
 * adds these; they're not in what we receive from the planner/rewriter.)
 *
 * For all query types, there can be additional junk tlist entries, such as
 * sort keys, Vars needed for a RETURNING list, and row ID information needed
 * for SELECT FOR UPDATE locking and/or EvalPlanQual checking.
 *
 * The query rewrite phase also does preprocessing of the targetlist (see
 * rewriteTargetListIU).  The division of labor between here and there is
 * partially historical, but it's not entirely arbitrary.  The stuff done
 * here is closely connected to physical access to tables, whereas the
 * rewriter's work is more concerned with SQL semantics.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/optimizer/prep/preptlist.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/table.h"
#include "nodes/makefuncs.h"
#include "optimizer/appendinfo.h"
#include "optimizer/optimizer.h"
#include "optimizer/prep.h"
#include "optimizer/tlist.h"
#include "parser/parse_coerce.h"
#include "parser/parsetree.h"
#include "utils/rel.h"

static List *expand_insert_targetlist(List *tlist, Relation rel);


/*
 * preprocess_targetlist
 *	  Driver for preprocessing the parse tree targetlist.
 *
 * The preprocessed targetlist is returned in root->processed_tlist.
 * Also, if this is an UPDATE, we return a list of target column numbers
 * in root->update_colnos.  (Resnos in processed_tlist will be consecutive,
 * so do not look at that to find out which columns are targets!)
 */
void
preprocess_targetlist(PlannerInfo *root)
{
	Query	   *parse = root->parse;
	int			result_relation = parse->resultRelation;
	List	   *range_table = parse->rtable;
	CmdType		command_type = parse->commandType;
	RangeTblEntry *target_rte = NULL;
	Relation	target_relation = NULL;
	List	   *tlist;
	ListCell   *lc;

	/*
	 * If there is a result relation, open it so we can look for missing
	 * columns and so on.  We assume that previous code already acquired at
	 * least AccessShareLock on the relation, so we need no lock here.
	 */
	if (result_relation)
	{
		target_rte = rt_fetch(result_relation, range_table);

		/*
		 * Sanity check: it'd better be a real relation not, say, a subquery.
		 * Else parser or rewriter messed up.
		 */
		if (target_rte->rtekind != RTE_RELATION)
			elog(ERROR, "result relation must be a regular relation");

		target_relation = table_open(target_rte->relid, NoLock);
	}
	else
		Assert(command_type == CMD_SELECT);

	/*
	 * In an INSERT, the executor expects the targetlist to match the exact
	 * order of the target table's attributes, including entries for
	 * attributes not mentioned in the source query.
	 *
	 * In an UPDATE, we don't rearrange the tlist order, but we need to make a
	 * separate list of the target attribute numbers, in tlist order, and then
	 * renumber the processed_tlist entries to be consecutive.
	 */
	tlist = parse->targetList;
	if (command_type == CMD_INSERT)
		tlist = expand_insert_targetlist(tlist, target_relation);
	else if (command_type == CMD_UPDATE)
		root->update_colnos = extract_update_targetlist_colnos(tlist);

	/*
	 * For non-inherited UPDATE/DELETE/MERGE, register any junk column(s)
	 * needed to allow the executor to identify the rows to be updated or
	 * deleted.  In the inheritance case, we do nothing now, leaving this to
	 * be dealt with when expand_inherited_rtentry() makes the leaf target
	 * relations.  (But there might not be any leaf target relations, in which
	 * case we must do this in distribute_row_identity_vars().)
	 */
	if ((command_type == CMD_UPDATE || command_type == CMD_DELETE ||
		 command_type == CMD_MERGE) &&
		!target_rte->inh)
	{
		/* row-identity logic expects to add stuff to processed_tlist */
		root->processed_tlist = tlist;
		add_row_identity_columns(root, result_relation,
								 target_rte, target_relation);
		tlist = root->processed_tlist;
	}

	/*
	 * For MERGE we also need to handle the target list for each INSERT and
	 * UPDATE action separately.  In addition, we examine the qual of each
	 * action and add any Vars there (other than those of the target rel) to
	 * the subplan targetlist.
	 */
	if (command_type == CMD_MERGE)
	{
		ListCell   *l;

		/*
		 * For MERGE, handle targetlist of each MergeAction separately. Give
		 * the same treatment to MergeAction->targetList as we would have
		 * given to a regular INSERT.  For UPDATE, collect the column numbers
		 * being modified.
		 */
		foreach(l, parse->mergeActionList)
		{
			MergeAction *action = (MergeAction *) lfirst(l);
			List	   *vars;
			ListCell   *l2;

			if (action->commandType == CMD_INSERT)
				action->targetList = expand_insert_targetlist(action->targetList,
															  target_relation);
			else if (action->commandType == CMD_UPDATE)
				action->updateColnos =
					extract_update_targetlist_colnos(action->targetList);

			/*
			 * Add resjunk entries for any Vars used in each action's
			 * targetlist and WHEN condition that belong to relations other
			 * than target.  Note that aggregates, window functions and
			 * placeholder vars are not possible anywhere in MERGE's WHEN
			 * clauses.  (PHVs may be added later, but they don't concern us
			 * here.)
			 */
			vars = pull_var_clause((Node *)
								   list_concat_copy((List *) action->qual,
													action->targetList),
								   0);
			foreach(l2, vars)
			{
				Var		   *var = (Var *) lfirst(l2);
				TargetEntry *tle;

				if (IsA(var, Var) && var->varno == result_relation)
					continue;	/* don't need it */

				if (tlist_member((Expr *) var, tlist))
					continue;	/* already got it */

				tle = makeTargetEntry((Expr *) var,
									  list_length(tlist) + 1,
									  NULL, true);
				tlist = lappend(tlist, tle);
			}
			list_free(vars);
		}
	}

	/*
	 * Add necessary junk columns for rowmarked rels.  These values are needed
	 * for locking of rels selected FOR UPDATE/SHARE, and to do EvalPlanQual
	 * rechecking.  See comments for PlanRowMark in plannodes.h.  If you
	 * change this stanza, see also expand_inherited_rtentry(), which has to
	 * be able to add on junk columns equivalent to these.
	 *
	 * (Someday it might be useful to fold these resjunk columns into the
	 * row-identity-column management used for UPDATE/DELETE.  Today is not
	 * that day, however.  One notable issue is that it seems important that
	 * the whole-row Vars made here use the real table rowtype, not RECORD, so
	 * that conversion to/from child relations' rowtypes will happen.  Also,
	 * since these entries don't potentially bloat with more and more child
	 * relations, there's not really much need for column sharing.)
	 */
	foreach(lc, root->rowMarks)
	{
		PlanRowMark *rc = (PlanRowMark *) lfirst(lc);
		Var		   *var;
		char		resname[32];
		TargetEntry *tle;

		/* child rels use the same junk attrs as their parents */
		if (rc->rti != rc->prti)
			continue;

		if (rc->allMarkTypes & ~(1 << ROW_MARK_COPY))
		{
			/* Need to fetch TID */
			var = makeVar(rc->rti,
						  SelfItemPointerAttributeNumber,
						  TIDOID,
						  -1,
						  InvalidOid,
						  0);
			snprintf(resname, sizeof(resname), "ctid%u", rc->rowmarkId);
			tle = makeTargetEntry((Expr *) var,
								  list_length(tlist) + 1,
								  pstrdup(resname),
								  true);
			tlist = lappend(tlist, tle);
		}
		if (rc->allMarkTypes & (1 << ROW_MARK_COPY))
		{
			/* Need the whole row as a junk var */
			var = makeWholeRowVar(rt_fetch(rc->rti, range_table),
								  rc->rti,
								  0,
								  false);
			snprintf(resname, sizeof(resname), "wholerow%u", rc->rowmarkId);
			tle = makeTargetEntry((Expr *) var,
								  list_length(tlist) + 1,
								  pstrdup(resname),
								  true);
			tlist = lappend(tlist, tle);
		}

		/* If parent of inheritance tree, always fetch the tableoid too. */
		if (rc->isParent)
		{
			var = makeVar(rc->rti,
						  TableOidAttributeNumber,
						  OIDOID,
						  -1,
						  InvalidOid,
						  0);
			snprintf(resname, sizeof(resname), "tableoid%u", rc->rowmarkId);
			tle = makeTargetEntry((Expr *) var,
								  list_length(tlist) + 1,
								  pstrdup(resname),
								  true);
			tlist = lappend(tlist, tle);
		}
	}

	/*
	 * If the query has a RETURNING list, add resjunk entries for any Vars
	 * used in RETURNING that belong to other relations.  We need to do this
	 * to make these Vars available for the RETURNING calculation.  Vars that
	 * belong to the result rel don't need to be added, because they will be
	 * made to refer to the actual heap tuple.
	 */
	if (parse->returningList && list_length(parse->rtable) > 1)
	{
		List	   *vars;
		ListCell   *l;

		vars = pull_var_clause((Node *) parse->returningList,
							   PVC_RECURSE_AGGREGATES |
							   PVC_RECURSE_WINDOWFUNCS |
							   PVC_INCLUDE_PLACEHOLDERS);
		foreach(l, vars)
		{
			Var		   *var = (Var *) lfirst(l);
			TargetEntry *tle;

			if (IsA(var, Var) &&
				var->varno == result_relation)
				continue;		/* don't need it */

			if (tlist_member((Expr *) var, tlist))
				continue;		/* already got it */

			tle = makeTargetEntry((Expr *) var,
								  list_length(tlist) + 1,
								  NULL,
								  true);

			tlist = lappend(tlist, tle);
		}
		list_free(vars);
	}

	root->processed_tlist = tlist;

	if (target_relation)
		table_close(target_relation, NoLock);
}

/*
 * extract_update_targetlist_colnos
 * 		Extract a list of the target-table column numbers that
 * 		an UPDATE's targetlist wants to assign to, then renumber.
 *
 * The convention in the parser and rewriter is that the resnos in an
 * UPDATE's non-resjunk TLE entries are the target column numbers
 * to assign to.  Here, we extract that info into a separate list, and
 * then convert the tlist to the sequential-numbering convention that's
 * used by all other query types.
 *
 * This is also applied to the tlist associated with INSERT ... ON CONFLICT
 * ... UPDATE, although not till much later in planning.
 */
List *
extract_update_targetlist_colnos(List *tlist)
{
	List	   *update_colnos = NIL;
	AttrNumber	nextresno = 1;
	ListCell   *lc;

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

		if (!tle->resjunk)
			update_colnos = lappend_int(update_colnos, tle->resno);
		tle->resno = nextresno++;
	}
	return update_colnos;
}


/*****************************************************************************
 *
 *		TARGETLIST EXPANSION
 *
 *****************************************************************************/

/*
 * expand_insert_targetlist
 *	  Given a target list as generated by the parser and a result relation,
 *	  add targetlist entries for any missing attributes, and ensure the
 *	  non-junk attributes appear in proper field order.
 *
 * Once upon a time we also did more or less this with UPDATE targetlists,
 * but now this code is only applied to INSERT targetlists.
 */
static List *
expand_insert_targetlist(List *tlist, Relation rel)
{
	List	   *new_tlist = NIL;
	ListCell   *tlist_item;
	int			attrno,
				numattrs;

	tlist_item = list_head(tlist);

	/*
	 * The rewriter should have already ensured that the TLEs are in correct
	 * order; but we have to insert TLEs for any missing attributes.
	 *
	 * Scan the tuple description in the relation's relcache entry to make
	 * sure we have all the user attributes in the right order.
	 */
	numattrs = RelationGetNumberOfAttributes(rel);

	for (attrno = 1; attrno <= numattrs; attrno++)
	{
		Form_pg_attribute att_tup = TupleDescAttr(rel->rd_att, attrno - 1);
		TargetEntry *new_tle = NULL;

		if (tlist_item != NULL)
		{
			TargetEntry *old_tle = (TargetEntry *) lfirst(tlist_item);

			if (!old_tle->resjunk && old_tle->resno == attrno)
			{
				new_tle = old_tle;
				tlist_item = lnext(tlist, tlist_item);
			}
		}

		if (new_tle == NULL)
		{
			/*
			 * Didn't find a matching tlist entry, so make one.
			 *
			 * INSERTs should insert NULL in this case.  (We assume the
			 * rewriter would have inserted any available non-NULL default
			 * value.)  Also, if the column isn't dropped, apply any domain
			 * constraints that might exist --- this is to catch domain NOT
			 * NULL.
			 *
			 * When generating a NULL constant for a dropped column, we label
			 * it INT4 (any other guaranteed-to-exist datatype would do as
			 * well). We can't label it with the dropped column's datatype
			 * since that might not exist anymore.  It does not really matter
			 * what we claim the type is, since NULL is NULL --- its
			 * representation is datatype-independent.  This could perhaps
			 * confuse code comparing the finished plan to the target
			 * relation, however.
			 */
			Oid			atttype = att_tup->atttypid;
			Oid			attcollation = att_tup->attcollation;
			Node	   *new_expr;

			if (!att_tup->attisdropped)
			{
				new_expr = (Node *) makeConst(atttype,
											  -1,
											  attcollation,
											  att_tup->attlen,
											  (Datum) 0,
											  true, /* isnull */
											  att_tup->attbyval);
				new_expr = coerce_to_domain(new_expr,
											InvalidOid, -1,
											atttype,
											COERCION_IMPLICIT,
											COERCE_IMPLICIT_CAST,
											-1,
											false);
			}
			else
			{
				/* Insert NULL for dropped column */
				new_expr = (Node *) makeConst(INT4OID,
											  -1,
											  InvalidOid,
											  sizeof(int32),
											  (Datum) 0,
											  true, /* isnull */
											  true /* byval */ );
			}

			new_tle = makeTargetEntry((Expr *) new_expr,
									  attrno,
									  pstrdup(NameStr(att_tup->attname)),
									  false);
		}

		new_tlist = lappend(new_tlist, new_tle);
	}

	/*
	 * The remaining tlist entries should be resjunk; append them all to the
	 * end of the new tlist, making sure they have resnos higher than the last
	 * real attribute.  (Note: although the rewriter already did such
	 * renumbering, we have to do it again here in case we added NULL entries
	 * above.)
	 */
	while (tlist_item)
	{
		TargetEntry *old_tle = (TargetEntry *) lfirst(tlist_item);

		if (!old_tle->resjunk)
			elog(ERROR, "targetlist is not sorted correctly");
		/* Get the resno right, but don't copy unnecessarily */
		if (old_tle->resno != attrno)
		{
			old_tle = flatCopyTargetEntry(old_tle);
			old_tle->resno = attrno;
		}
		new_tlist = lappend(new_tlist, old_tle);
		attrno++;
		tlist_item = lnext(tlist, tlist_item);
	}

	return new_tlist;
}


/*
 * Locate PlanRowMark for given RT index, or return NULL if none
 *
 * This probably ought to be elsewhere, but there's no very good place
 */
PlanRowMark *
get_plan_rowmark(List *rowmarks, Index rtindex)
{
	ListCell   *l;

	foreach(l, rowmarks)
	{
		PlanRowMark *rc = (PlanRowMark *) lfirst(l);

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