During ALTER TABLE ADD FOREIGN KEY, try to check the existing rows using

a single LEFT JOIN query instead of firing the check trigger for each
row individually.  Stephan Szabo, with some kibitzing from Tom Lane and
Jan Wieck.

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.85 2003/10/02 06:36:37 petere Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.86 2003/10/06 16:38:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3454,6 +3454,13 @@ validateForeignKeyConstraint(FkConstraint *fkconstraint,
 	List	   *list;
 	int			count;
 
+	/*
+	 * See if we can do it with a single LEFT JOIN query.  A FALSE result
+	 * indicates we must proceed with the fire-the-trigger method.
+	 */
+	if (RI_Initial_Check(fkconstraint, rel, pkrel))
+		return;
+
 	/*
 	 * Scan through each tuple, calling RI_FKey_check_ins (insert trigger)
 	 * as if that tuple had just been inserted.  If any of those fail, it

src/backend/utils/adt/ri_triggers.c

@@ -17,7 +17,7 @@
  *
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  *
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/ri_triggers.c,v 1.61 2003/10/01 21:30:52 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/ri_triggers.c,v 1.62 2003/10/06 16:38:28 tgl Exp $
  *
  * ----------
  */
@@ -40,6 +40,7 @@
 #include "rewrite/rewriteHandler.h"
 #include "utils/lsyscache.h"
 #include "utils/typcache.h"
+#include "utils/acl.h"
 #include "miscadmin.h"
 
 
@@ -164,7 +165,8 @@ static void ri_ExtractValues(RI_QueryKey *qkey, int key_idx,
 				 Datum *vals, char *nulls);
 static void ri_ReportViolation(RI_QueryKey *qkey, const char *constrname,
 				   Relation pk_rel, Relation fk_rel,
-				   HeapTuple violator, bool spi_err);
+				   HeapTuple violator, TupleDesc tupdesc,
+				   bool spi_err);
 
 
 /* ----------
@@ -2540,7 +2542,205 @@ RI_FKey_keyequal_upd(TriggerData *trigdata)
 }
 
 
+/* ----------
+ * RI_Initial_Check -
+ *
+ *	Check an entire table for non-matching values using a single query.
+ *	This is not a trigger procedure, but is called during ALTER TABLE
+ *	ADD FOREIGN KEY to validate the initial table contents.
+ *
+ *	We expect that an exclusive lock has been taken on rel and pkrel;
+ *	hence, we do not need to lock individual rows for the check.
+ *
+ *	If the check fails because the current user doesn't have permissions
+ *	to read both tables, return false to let our caller know that they will
+ *	need to do something else to check the constraint.
+ * ----------
+ */
+bool
+RI_Initial_Check(FkConstraint *fkconstraint, Relation rel, Relation pkrel)
+{
+	const char *constrname = fkconstraint->constr_name;
+	char		querystr[MAX_QUOTED_REL_NAME_LEN * 2 + 250 +
+						(MAX_QUOTED_NAME_LEN + 32) * ((RI_MAX_NUMKEYS * 4)+1)];
+	char		pkrelname[MAX_QUOTED_REL_NAME_LEN];
+	char		relname[MAX_QUOTED_REL_NAME_LEN];
+	char		attname[MAX_QUOTED_NAME_LEN];
+	char		fkattname[MAX_QUOTED_NAME_LEN];
+	const char *sep;
+	List		*list;
+	List		*list2;
+	int			spi_result;
+	void		*qplan;
+
+	/*
+	 * Check to make sure current user has enough permissions to do the
+	 * test query.  (If not, caller can fall back to the trigger method,
+	 * which works because it changes user IDs on the fly.)
+	 *
+	 * XXX are there any other show-stopper conditions to check?
+	 */
+	if (pg_class_aclcheck(RelationGetRelid(rel), GetUserId(), ACL_SELECT) != ACLCHECK_OK)
+		return false;
+	if (pg_class_aclcheck(RelationGetRelid(pkrel), GetUserId(), ACL_SELECT) != ACLCHECK_OK) 
+		return false;
+
+	/*----------
+	 * The query string built is:
+	 *  SELECT fk.keycols FROM ONLY relname fk 
+	 *   LEFT OUTER JOIN ONLY pkrelname pk 
+	 *   ON (pk.pkkeycol1=fk.keycol1 [AND ...])
+	 *   WHERE pk.pkkeycol1 IS NULL AND
+	 * For MATCH unspecified:
+	 *   (fk.keycol1 IS NOT NULL [AND ...])
+	 * For MATCH FULL:
+	 *   (fk.keycol1 IS NOT NULL [OR ...])
+	 *----------
+	 */
+
+	sprintf(querystr, "SELECT ");
+	sep="";
+	foreach(list, fkconstraint->fk_attrs)
+	{
+		quoteOneName(attname, strVal(lfirst(list)));
+		snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+				 "%sfk.%s", sep, attname);
+		sep = ", ";
+	}
+
+	quoteRelationName(pkrelname, pkrel);
+	quoteRelationName(relname, rel);
+	snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+			 " FROM ONLY %s fk LEFT OUTER JOIN ONLY %s pk ON (",
+			 relname, pkrelname);
+
+	sep="";
+	for (list=fkconstraint->pk_attrs, list2=fkconstraint->fk_attrs; 
+		 list != NIL && list2 != NIL; 
+		 list=lnext(list), list2=lnext(list2))
+	{
+		quoteOneName(attname, strVal(lfirst(list)));
+		quoteOneName(fkattname, strVal(lfirst(list2)));
+		snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+				 "%spk.%s=fk.%s",
+				 sep, attname, fkattname);
+		sep = " AND ";
+	}
+	/*
+	 * It's sufficient to test any one pk attribute for null to detect a
+	 * join failure.
+	 */
+	quoteOneName(attname, strVal(lfirst(fkconstraint->pk_attrs)));
+	snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+			 ") WHERE pk.%s IS NULL AND (", attname);
+
+	sep="";
+	foreach(list, fkconstraint->fk_attrs)
+	{
+		quoteOneName(attname, strVal(lfirst(list)));
+		snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+				 "%sfk.%s IS NOT NULL",
+				 sep, attname);
+		switch (fkconstraint->fk_matchtype)
+		{
+			case FKCONSTR_MATCH_UNSPECIFIED:
+				sep=" AND ";
+				break;
+			case FKCONSTR_MATCH_FULL:
+				sep=" OR ";
+				break;
+			case FKCONSTR_MATCH_PARTIAL:
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("MATCH PARTIAL not yet implemented")));
+				break;
+			default:
+				elog(ERROR, "unrecognized match type: %d",
+					 fkconstraint->fk_matchtype);
+				break;
+		}
+	}
+	snprintf(querystr + strlen(querystr), sizeof(querystr) - strlen(querystr),
+			 ")");
+
+	if (SPI_connect() != SPI_OK_CONNECT)
+		elog(ERROR, "SPI_connect failed");
 
+	/*
+	 * Generate the plan.  We don't need to cache it, and there are no
+	 * arguments to the plan. 
+	 */
+	qplan = SPI_prepare(querystr, 0, NULL);
+
+	if (qplan == NULL)
+		elog(ERROR, "SPI_prepare returned %d for %s", SPI_result, querystr);
+
+	/*
+	 * Run the plan.  For safety we force a current query snapshot to be
+	 * used.  (In serializable mode, this arguably violates serializability,
+	 * but we really haven't got much choice.)  We need at most one tuple
+	 * returned, so pass limit = 1.
+	 */
+	spi_result = SPI_execp_current(qplan, NULL, NULL, true, 1);
+
+	/* Check result */
+	if (spi_result != SPI_OK_SELECT)
+		elog(ERROR, "SPI_execp_current returned %d", spi_result);
+
+	/* Did we find a tuple violating the constraint? */
+	if (SPI_processed > 0)
+	{
+		HeapTuple	tuple = SPI_tuptable->vals[0];
+		TupleDesc	tupdesc = SPI_tuptable->tupdesc;
+		int			nkeys = length(fkconstraint->fk_attrs);
+		int			i;
+		RI_QueryKey	qkey;
+
+		/*
+		 * If it's MATCH FULL, and there are any nulls in the FK keys,
+		 * complain about that rather than the lack of a match.  MATCH FULL
+		 * disallows partially-null FK rows.
+		 */
+		if (fkconstraint->fk_matchtype == FKCONSTR_MATCH_FULL)
+		{
+			bool	isnull = false;
+
+			for (i = 1; i <= nkeys; i++)
+			{
+				(void) SPI_getbinval(tuple, tupdesc, i, &isnull);
+				if (isnull)
+					break;
+			}
+			if (isnull)
+				ereport(ERROR,
+						(errcode(ERRCODE_FOREIGN_KEY_VIOLATION),
+						 errmsg("insert or update on table \"%s\" violates foreign key constraint \"%s\"",
+								RelationGetRelationName(rel),
+								constrname),
+						 errdetail("MATCH FULL does not allow mixing of null and nonnull key values.")));
+		}
+
+		/*
+		 * Although we didn't cache the query, we need to set up a fake
+		 * query key to pass to ri_ReportViolation.
+		 */
+		MemSet(&qkey, 0, sizeof(qkey));
+		qkey.constr_queryno = RI_PLAN_CHECK_LOOKUPPK;
+		qkey.nkeypairs = nkeys;
+		for (i = 0; i < nkeys; i++)
+			qkey.keypair[i][RI_KEYPAIR_FK_IDX] = i + 1;
+
+		ri_ReportViolation(&qkey, constrname,
+						   pkrel, rel,
+						   tuple, tupdesc,
+						   false);
+	}
+
+	if (SPI_finish() != SPI_OK_FINISH)
+		elog(ERROR, "SPI_finish failed");
+
+	return true;
+}
 
 
 /* ----------
@@ -2782,6 +2982,9 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 	/* Create the plan */
 	qplan = SPI_prepare(querystr, nargs, argtypes);
 
+	if (qplan == NULL)
+		elog(ERROR, "SPI_prepare returned %d for %s", SPI_result, querystr);
+
 	/* Restore UID */
 	SetUserId(save_uid);
 
@@ -2905,6 +3108,7 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 		ri_ReportViolation(qkey, constrname ? constrname : "",
 						   pk_rel, fk_rel,
 						   new_tuple ? new_tuple : old_tuple,
+						   NULL,
 						   true);
 
 	/* XXX wouldn't it be clearer to do this part at the caller? */
@@ -2913,6 +3117,7 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 		ri_ReportViolation(qkey, constrname,
 						   pk_rel, fk_rel,
 						   new_tuple ? new_tuple : old_tuple,
+						   NULL,
 						   false);
 
 	return SPI_processed != 0;
@@ -2950,7 +3155,8 @@ ri_ExtractValues(RI_QueryKey *qkey, int key_idx,
 static void
 ri_ReportViolation(RI_QueryKey *qkey, const char *constrname,
 				   Relation pk_rel, Relation fk_rel,
-				   HeapTuple violator, bool spi_err)
+				   HeapTuple violator, TupleDesc tupdesc,
+				   bool spi_err)
 {
 #define BUFLENGTH	512
 	char		key_names[BUFLENGTH];
@@ -2958,7 +3164,6 @@ ri_ReportViolation(RI_QueryKey *qkey, const char *constrname,
 	char	   *name_ptr = key_names;
 	char	   *val_ptr = key_values;
 	bool		onfk;
-	Relation	rel;
 	int			idx,
 				key_idx;
 
@@ -2972,18 +3177,21 @@ ri_ReportViolation(RI_QueryKey *qkey, const char *constrname,
 				 errhint("This is most likely due to a rule having rewritten the query.")));
 
 	/*
-	 * rel is set to where the tuple description is coming from.
+	 * Determine which relation to complain about.  If tupdesc wasn't
+	 * passed by caller, assume the violator tuple came from there.
 	 */
 	onfk = (qkey->constr_queryno == RI_PLAN_CHECK_LOOKUPPK);
 	if (onfk)
 	{
-		rel = fk_rel;
 		key_idx = RI_KEYPAIR_FK_IDX;
+		if (tupdesc == NULL)
+			tupdesc = fk_rel->rd_att;
 	}
 	else
 	{
-		rel = pk_rel;
 		key_idx = RI_KEYPAIR_PK_IDX;
+		if (tupdesc == NULL)
+			tupdesc = pk_rel->rd_att;
 	}
 
 	/*
@@ -3008,8 +3216,8 @@ ri_ReportViolation(RI_QueryKey *qkey, const char *constrname,
 		char	   *name,
 				   *val;
 
-		name = SPI_fname(rel->rd_att, fnum);
-		val = SPI_getvalue(violator, rel->rd_att, fnum);
+		name = SPI_fname(tupdesc, fnum);
+		val = SPI_getvalue(violator, tupdesc, fnum);
 		if (!val)
 			val = "null";
 

src/include/commands/trigger.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: trigger.h,v 1.43 2003/08/04 02:40:13 momjian Exp $
+ * $Id: trigger.h,v 1.44 2003/10/06 16:38:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -197,5 +197,8 @@ extern void DeferredTriggerSetState(ConstraintsSetStmt *stmt);
  * in utils/adt/ri_triggers.c
  */
 extern bool RI_FKey_keyequal_upd(TriggerData *trigdata);
+extern bool RI_Initial_Check(FkConstraint *fkconstraint, 
+							 Relation rel, 
+							 Relation pkrel);
 
 #endif   /* TRIGGER_H */