Provide the OR REPLACE option for CREATE TRIGGER.

This is mostly straightforward.  However, we disallow replacing
constraint triggers or changing the is-constraint property; perhaps
that can be added later, but the complexity versus benefit tradeoff
doesn't look very good.

Also, no special thought is taken here for whether replacing an
existing trigger should result in changes to queued-but-not-fired
trigger actions.  We just document that if you're surprised by the
results, too bad, don't do that.  (Note that any such pending trigger
activity would have to be within the current session.)

Takamichi Osumi, reviewed at various times by Surafel Temesgen,
Peter Smith, and myself

Discussion: https://postgr.es/m/0DDF369B45A1B44B8A687ED43F06557C010BC362@G01JPEXMBYT03

1 files changed, 16 insertions, 12 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index e3cfaf8b074..46f1637e774 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -10550,10 +10550,10 @@ CreateFKCheckTrigger(Oid myRelOid, Oid refRelOid, Constraint *fkconstraint,
 	 * and "RI_ConstraintTrigger_c_NNNN" for the check triggers.
 	 */
 	fk_trigger = makeNode(CreateTrigStmt);
+	fk_trigger->replace = false;
+	fk_trigger->isconstraint = true;
 	fk_trigger->trigname = "RI_ConstraintTrigger_c";
 	fk_trigger->relation = NULL;
-	fk_trigger->row = true;
-	fk_trigger->timing = TRIGGER_TYPE_AFTER;
 
 	/* Either ON INSERT or ON UPDATE */
 	if (on_insert)
@@ -10567,14 +10567,15 @@ CreateFKCheckTrigger(Oid myRelOid, Oid refRelOid, Constraint *fkconstraint,
 		fk_trigger->events = TRIGGER_TYPE_UPDATE;
 	}
 
+	fk_trigger->args = NIL;
+	fk_trigger->row = true;
+	fk_trigger->timing = TRIGGER_TYPE_AFTER;
 	fk_trigger->columns = NIL;
-	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
+	fk_trigger->transitionRels = NIL;
 	fk_trigger->deferrable = fkconstraint->deferrable;
 	fk_trigger->initdeferred = fkconstraint->initdeferred;
 	fk_trigger->constrrel = NULL;
-	fk_trigger->args = NIL;
 
 	(void) CreateTrigger(fk_trigger, NULL, myRelOid, refRelOid, constraintOid,
 						 indexOid, InvalidOid, InvalidOid, NULL, true, false);
@@ -10599,15 +10600,17 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 	 * DELETE action on the referenced table.
 	 */
 	fk_trigger = makeNode(CreateTrigStmt);
+	fk_trigger->replace = false;
+	fk_trigger->isconstraint = true;
 	fk_trigger->trigname = "RI_ConstraintTrigger_a";
 	fk_trigger->relation = NULL;
+	fk_trigger->args = NIL;
 	fk_trigger->row = true;
 	fk_trigger->timing = TRIGGER_TYPE_AFTER;
 	fk_trigger->events = TRIGGER_TYPE_DELETE;
 	fk_trigger->columns = NIL;
-	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
+	fk_trigger->transitionRels = NIL;
 	fk_trigger->constrrel = NULL;
 	switch (fkconstraint->fk_del_action)
 	{
@@ -10641,7 +10644,6 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 				 (int) fkconstraint->fk_del_action);
 			break;
 	}
-	fk_trigger->args = NIL;
 
 	(void) CreateTrigger(fk_trigger, NULL, refRelOid, RelationGetRelid(rel),
 						 constraintOid,
@@ -10655,15 +10657,17 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 	 * UPDATE action on the referenced table.
 	 */
 	fk_trigger = makeNode(CreateTrigStmt);
+	fk_trigger->replace = false;
+	fk_trigger->isconstraint = true;
 	fk_trigger->trigname = "RI_ConstraintTrigger_a";
 	fk_trigger->relation = NULL;
+	fk_trigger->args = NIL;
 	fk_trigger->row = true;
 	fk_trigger->timing = TRIGGER_TYPE_AFTER;
 	fk_trigger->events = TRIGGER_TYPE_UPDATE;
 	fk_trigger->columns = NIL;
-	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
+	fk_trigger->transitionRels = NIL;
 	fk_trigger->constrrel = NULL;
 	switch (fkconstraint->fk_upd_action)
 	{
@@ -10697,7 +10701,6 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 				 (int) fkconstraint->fk_upd_action);
 			break;
 	}
-	fk_trigger->args = NIL;
 
 	(void) CreateTrigger(fk_trigger, NULL, refRelOid, RelationGetRelid(rel),
 						 constraintOid,
@@ -16898,6 +16901,8 @@ CloneRowTriggersToPartition(Relation parent, Relation partition)
 		}
 
 		trigStmt = makeNode(CreateTrigStmt);
+		trigStmt->replace = false;
+		trigStmt->isconstraint = OidIsValid(trigForm->tgconstraint);
 		trigStmt->trigname = NameStr(trigForm->tgname);
 		trigStmt->relation = NULL;
 		trigStmt->funcname = NULL;	/* passed separately */
@@ -16907,7 +16912,6 @@ CloneRowTriggersToPartition(Relation parent, Relation partition)
 		trigStmt->events = trigForm->tgtype & TRIGGER_TYPE_EVENT_MASK;
 		trigStmt->columns = cols;
 		trigStmt->whenClause = NULL;	/* passed separately */
-		trigStmt->isconstraint = OidIsValid(trigForm->tgconstraint);
 		trigStmt->transitionRels = NIL; /* not supported at present */
 		trigStmt->deferrable = trigForm->tgdeferrable;
 		trigStmt->initdeferred = trigForm->tginitdeferred;