CREATE_OR_REPLACE_TRIGGER_v06.patch

diff --git a/doc/src/sgml/ref/create_trigger.sgml b/doc/src/sgml/ref/create_trigger.sgml
index bde3a63..675e3b6 100644
--- a/doc/src/sgml/ref/create_trigger.sgml
+++ b/doc/src/sgml/ref/create_trigger.sgml
@@ -26,7 +26,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE [ CONSTRAINT ] TRIGGER <replaceable class="parameter">name</replaceable> { BEFORE | AFTER | INSTEAD OF } { <replaceable class="parameter">event</replaceable> [ OR ... ] }
+CREATE [ OR REPLACE ] [ CONSTRAINT ] TRIGGER <replaceable class="parameter">name</replaceable> { BEFORE | AFTER | INSTEAD OF } { <replaceable class="parameter">event</replaceable> [ OR ... ] }
     ON <replaceable class="parameter">table_name</replaceable>
     [ FROM <replaceable class="parameter">referenced_table_name</replaceable> ]
     [ NOT DEFERRABLE | [ DEFERRABLE ] [ INITIALLY IMMEDIATE | INITIALLY DEFERRED ] ]
diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 632c058..fefea5d 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2404,7 +2404,8 @@ StoreRelCheck(Relation rel, const char *ccname, Node *expr,
 	 * Create the Check Constraint
 	 */
 	constrOid =
-		CreateConstraintEntry(ccname,	/* Constraint Name */
+		CreateConstraintEntry(InvalidOid,
+							  ccname,	/* Constraint Name */
 							  RelationGetNamespace(rel),	/* namespace */
 							  CONSTRAINT_CHECK, /* Constraint Type */
 							  false,	/* Is Deferrable */
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index bd7ec92..3c2a503 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1873,7 +1873,8 @@ index_constraint_create(Relation heapRelation,
 	/*
 	 * Construct a pg_constraint entry.
 	 */
-	conOid = CreateConstraintEntry(constraintName,
+	conOid = CreateConstraintEntry(InvalidOid,
+								   constraintName,
 								   namespaceId,
 								   constraintType,
 								   deferrable,
@@ -1938,6 +1939,8 @@ index_constraint_create(Relation heapRelation,
 		CreateTrigStmt *trigger;
 
 		trigger = makeNode(CreateTrigStmt);
+		trigger->replace = false;
+		trigger->isconstraint = true;
 		trigger->trigname = (constraintType == CONSTRAINT_PRIMARY) ?
 			"PK_ConstraintTrigger" :
 			"Unique_ConstraintTrigger";
@@ -1949,7 +1952,6 @@ index_constraint_create(Relation heapRelation,
 		trigger->events = TRIGGER_TYPE_INSERT | TRIGGER_TYPE_UPDATE;
 		trigger->columns = NIL;
 		trigger->whenClause = NULL;
-		trigger->isconstraint = true;
 		trigger->deferrable = true;
 		trigger->initdeferred = initdeferred;
 		trigger->constrrel = NULL;
diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 90932be..dc801a7 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -44,10 +44,12 @@
  * constraint) are *not* created here.  But we do make dependency links
  * from the constraint to the things it depends on.
  *
- * The new constraint's OID is returned.
+ * The new constraint's OID is returned. (This will be the same as
+ * "conOid" if that is specified as nonzero.)
  */
 Oid
-CreateConstraintEntry(const char *constraintName,
+CreateConstraintEntry(Oid existing_constraint_oid,
+					  const char *constraintName,
 					  Oid constraintNamespace,
 					  char constraintType,
 					  bool isDeferrable,
@@ -78,7 +80,7 @@ CreateConstraintEntry(const char *constraintName,
 					  bool is_internal)
 {
 	Relation	conDesc;
-	Oid			conOid;
+	Oid			conOid = InvalidOid;
 	HeapTuple	tup;
 	bool		nulls[Natts_pg_constraint];
 	Datum		values[Natts_pg_constraint];
@@ -91,7 +93,12 @@ CreateConstraintEntry(const char *constraintName,
 	NameData	cname;
 	int			i;
 	ObjectAddress conobject;
-
+	SysScanDesc   conscan;
+	ScanKeyData   skey[2];
+	HeapTuple     tuple;
+	bool          replaces[Natts_pg_constraint];
+	Form_pg_constraint constrForm;
+	
 	conDesc = table_open(ConstraintRelationId, RowExclusiveLock);
 
 	Assert(constraintName);
@@ -163,9 +170,12 @@ CreateConstraintEntry(const char *constraintName,
 		values[i] = (Datum) NULL;
 	}
 
-	conOid = GetNewOidWithIndex(conDesc, ConstraintOidIndexId,
-								Anum_pg_constraint_oid);
-	values[Anum_pg_constraint_oid - 1] = ObjectIdGetDatum(conOid);
+	if (!existing_constraint_oid)
+	{
+		conOid = GetNewOidWithIndex(conDesc, ConstraintOidIndexId,
+									Anum_pg_constraint_oid);
+		values[Anum_pg_constraint_oid - 1] = ObjectIdGetDatum(conOid);
+	}
 	values[Anum_pg_constraint_conname - 1] = NameGetDatum(&cname);
 	values[Anum_pg_constraint_connamespace - 1] = ObjectIdGetDatum(constraintNamespace);
 	values[Anum_pg_constraint_contype - 1] = CharGetDatum(constraintType);
@@ -219,9 +229,47 @@ CreateConstraintEntry(const char *constraintName,
 	else
 		nulls[Anum_pg_constraint_conbin - 1] = true;
 
-	tup = heap_form_tuple(RelationGetDescr(conDesc), values, nulls);
+	if (OidIsValid(existing_constraint_oid))
+	{
+		ScanKeyInit(&skey[0],
+					Anum_pg_constraint_oid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(existing_constraint_oid));
+
+		conscan = systable_beginscan(conDesc,
+						 ConstraintOidIndexId,
+						 true,
+						 NULL,
+						 1,
+						 skey);
+
+		tuple = systable_getnext(conscan);
+		Assert (HeapTupleIsValid(tuple));
+		constrForm = (Form_pg_constraint) GETSTRUCT(tuple);
+		conOid = constrForm->oid;
+		Assert(conOid == existing_constraint_oid);
+
+		memset(replaces, true, sizeof(replaces));
+		replaces[Anum_pg_constraint_oid - 1] = false; /* skip updating Oid data */
+		replaces[Anum_pg_constraint_conname - 1] = false;
+		replaces[Anum_pg_constraint_confrelid - 1] = false;
+
+		/* Modify the existing constraint entry */
+		tup = heap_modify_tuple(tuple, RelationGetDescr(conDesc), values, nulls, replaces);
+		CatalogTupleUpdate(conDesc, &tuple->t_self, tup);
+		heap_freetuple(tup);
 
-	CatalogTupleInsert(conDesc, tup);
+		/* Remove all old dependencies before registering new ones */
+		deleteDependencyRecordsFor(ConstraintRelationId, conOid, true);
+
+		systable_endscan(conscan);
+	}
+	else
+	{
+		tup = heap_form_tuple(RelationGetDescr(conDesc), values, nulls);
+		CatalogTupleInsert(conDesc, tup);
+		heap_freetuple(tup);
+	}
 
 	conobject.classId = ConstraintRelationId;
 	conobject.objectId = conOid;
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 037d457..3481ced 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8583,7 +8583,8 @@ addFkRecurseReferenced(List **wqueue, Constraint *fkconstraint, Relation rel,
 	/*
 	 * Record the FK constraint in pg_constraint.
 	 */
-	constrOid = CreateConstraintEntry(conname,
+	constrOid = CreateConstraintEntry(InvalidOid,
+									  conname,
 									  RelationGetNamespace(rel),
 									  CONSTRAINT_FOREIGN,
 									  fkconstraint->deferrable,
@@ -8611,7 +8612,7 @@ addFkRecurseReferenced(List **wqueue, Constraint *fkconstraint, Relation rel,
 									  conislocal,	/* islocal */
 									  coninhcount,	/* inhcount */
 									  connoinherit, /* conNoInherit */
-									  false);	/* is_internal */
+									  false); /* is_internal */
 
 	ObjectAddressSet(address, ConstraintRelationId, constrOid);
 
@@ -8851,7 +8852,8 @@ addFkRecurseReferencing(List **wqueue, Constraint *fkconstraint, Relation rel,
 			else
 				conname = fkconstraint->conname;
 			constrOid =
-				CreateConstraintEntry(conname,
+				CreateConstraintEntry(InvalidOid,
+									  conname,
 									  RelationGetNamespace(partition),
 									  CONSTRAINT_FOREIGN,
 									  fkconstraint->deferrable,
@@ -9253,7 +9255,8 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
 
 		indexOid = constrForm->conindid;
 		constrOid =
-			CreateConstraintEntry(fkconstraint->conname,
+			CreateConstraintEntry(InvalidOid,
+								  fkconstraint->conname,
 								  constrForm->connamespace,
 								  CONSTRAINT_FOREIGN,
 								  fkconstraint->deferrable,
@@ -10319,6 +10322,8 @@ 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;
@@ -10339,7 +10344,6 @@ CreateFKCheckTrigger(Oid myRelOid, Oid refRelOid, Constraint *fkconstraint,
 	fk_trigger->columns = NIL;
 	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
 	fk_trigger->deferrable = fkconstraint->deferrable;
 	fk_trigger->initdeferred = fkconstraint->initdeferred;
 	fk_trigger->constrrel = NULL;
@@ -10368,6 +10372,8 @@ 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->row = true;
@@ -10376,7 +10382,6 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 	fk_trigger->columns = NIL;
 	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
 	fk_trigger->constrrel = NULL;
 	switch (fkconstraint->fk_del_action)
 	{
@@ -10424,6 +10429,8 @@ 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->row = true;
@@ -10432,7 +10439,6 @@ createForeignKeyActionTriggers(Relation rel, Oid refRelOid, Constraint *fkconstr
 	fk_trigger->columns = NIL;
 	fk_trigger->transitionRels = NIL;
 	fk_trigger->whenClause = NULL;
-	fk_trigger->isconstraint = true;
 	fk_trigger->constrrel = NULL;
 	switch (fkconstraint->fk_upd_action)
 	{
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index ed551ab..4fc446b 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -31,6 +31,7 @@
 #include "catalog/pg_proc.h"
 #include "catalog/pg_trigger.h"
 #include "catalog/pg_type.h"
+#include "catalog/pg_depend.h"
 #include "commands/dbcommands.h"
 #include "commands/defrem.h"
 #include "commands/trigger.h"
@@ -175,7 +176,7 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	Relation	pgrel;
 	HeapTuple	tuple;
 	Oid			funcrettype;
-	Oid			trigoid;
+	Oid			trigoid = InvalidOid;
 	char		internaltrigname[NAMEDATALEN];
 	char	   *trigname;
 	Oid			constrrelid = InvalidOid;
@@ -184,6 +185,12 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	char	   *oldtablename = NULL;
 	char	   *newtablename = NULL;
 	bool		partition_recurse;
+	bool		is_update = false;
+	HeapTuple	newtup;
+	TupleDesc	tupDesc;
+	bool		replaces[Natts_pg_trigger];
+	Oid		existing_constraint_oid = InvalidOid;
+	bool		trigger_exists = false;
 
 	if (OidIsValid(relOid))
 		rel = table_open(relOid, ShareRowExclusiveLock);
@@ -668,6 +675,64 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 		whenRtable = NIL;
 	}
 
+	/* Check if there is a pre-existing trigger of the same name */
+	tgrel = table_open(TriggerRelationId, RowExclusiveLock);
+	if(!isInternal)
+	{
+		ScanKeyInit(&key,
+					Anum_pg_trigger_tgrelid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(RelationGetRelid(rel)));
+		tgscan = systable_beginscan(tgrel, TriggerRelidNameIndexId, true,
+									NULL, 1, &key);
+		while (HeapTupleIsValid(tuple = systable_getnext(tgscan)))
+		{
+			Form_pg_trigger pg_trigger = (Form_pg_trigger) GETSTRUCT(tuple);
+
+			if (namestrcmp(&(pg_trigger->tgname), stmt->trigname) == 0)
+			{
+				/* Store values for replacement of this trigger */
+				trigoid = pg_trigger->oid;
+				existing_constraint_oid = pg_trigger->tgconstraint;
+				trigger_exists = true;
+				break;
+			}
+		}
+		systable_endscan(tgscan);
+	}
+
+	/* Generate the trigger's oid because there was no same name trigger. */
+	if (!trigger_exists)
+		trigoid = GetNewOidWithIndex(tgrel, TriggerOidIndexId,
+									 Anum_pg_trigger_oid);
+	else
+	{
+		/*
+		 * without OR REPLACE clause, can't override the trigger with the same name.
+		 */
+		if (!stmt->replace && !isInternal)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("trigger \"%s\" for relation \"%s\" already exists",
+							stmt->trigname, RelationGetRelationName(rel))));
+		/*
+		 * CREATE OR REPLACE CONSTRAINT TRIGGER command can't replace non-constraint trigger.
+		 */
+		if (stmt->replace && stmt->isconstraint && !OidIsValid(existing_constraint_oid))
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("Trigger \"%s\" for relation \"%s\" cannot be replaced with constraint trigger",
+							stmt->trigname, RelationGetRelationName(rel))));
+		/*
+		 * CREATE OR REPLACE TRIGGER command can't replace constraint trigger.
+		 */
+		if (stmt->replace && !stmt->isconstraint && OidIsValid(existing_constraint_oid))
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("Constraint trigger \"%s\" for relation \"%s\" cannot be replaced with non-constraint trigger",
+							stmt->trigname, RelationGetRelationName(rel))));
+	}
+
 	/*
 	 * Find and validate the trigger function.
 	 */
@@ -695,7 +760,8 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	{
 		/* Internal callers should have made their own constraints */
 		Assert(!isInternal);
-		constraintOid = CreateConstraintEntry(stmt->trigname,
+		constraintOid = CreateConstraintEntry(existing_constraint_oid,
+											  stmt->trigname,
 											  RelationGetNamespace(rel),
 											  CONSTRAINT_TRIGGER,
 											  stmt->deferrable,
@@ -727,15 +793,6 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	}
 
 	/*
-	 * Generate the trigger's OID now, so that we can use it in the name if
-	 * needed.
-	 */
-	tgrel = table_open(TriggerRelationId, RowExclusiveLock);
-
-	trigoid = GetNewOidWithIndex(tgrel, TriggerOidIndexId,
-								 Anum_pg_trigger_oid);
-
-	/*
 	 * If trigger is internally generated, modify the provided trigger name to
 	 * ensure uniqueness by appending the trigger OID.  (Callers will usually
 	 * supply a simple constant trigger name in these cases.)
@@ -753,37 +810,6 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	}
 
 	/*
-	 * Scan pg_trigger for existing triggers on relation.  We do this only to
-	 * give a nice error message if there's already a trigger of the same
-	 * name.  (The unique index on tgrelid/tgname would complain anyway.) We
-	 * can skip this for internally generated triggers, since the name
-	 * modification above should be sufficient.
-	 *
-	 * NOTE that this is cool only because we have ShareRowExclusiveLock on
-	 * the relation, so the trigger set won't be changing underneath us.
-	 */
-	if (!isInternal)
-	{
-		ScanKeyInit(&key,
-					Anum_pg_trigger_tgrelid,
-					BTEqualStrategyNumber, F_OIDEQ,
-					ObjectIdGetDatum(RelationGetRelid(rel)));
-		tgscan = systable_beginscan(tgrel, TriggerRelidNameIndexId, true,
-									NULL, 1, &key);
-		while (HeapTupleIsValid(tuple = systable_getnext(tgscan)))
-		{
-			Form_pg_trigger pg_trigger = (Form_pg_trigger) GETSTRUCT(tuple);
-
-			if (namestrcmp(&(pg_trigger->tgname), trigname) == 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DUPLICATE_OBJECT),
-						 errmsg("trigger \"%s\" for relation \"%s\" already exists",
-								trigname, RelationGetRelationName(rel))));
-		}
-		systable_endscan(tgscan);
-	}
-
-	/*
 	 * Build the new pg_trigger tuple.
 	 *
 	 * When we're creating a trigger in a partition, we mark it as internal,
@@ -911,12 +937,51 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 
 	tuple = heap_form_tuple(tgrel->rd_att, values, nulls);
 
-	/*
-	 * Insert tuple into pg_trigger.
-	 */
-	CatalogTupleInsert(tgrel, tuple);
+	if (!trigger_exists)
+	{
+		tuple = heap_form_tuple(tgrel->rd_att, values, nulls);
+
+		/*
+		 * Insert tuple into pg_trigger.
+		 */
+		CatalogTupleInsert(tgrel, tuple);
+
+		heap_freetuple(tuple);
+	}
+	else
+	{
+		memset(replaces, true, sizeof(replaces));
+
+		ScanKeyInit(&key,
+				Anum_pg_trigger_tgrelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(rel)));
+		tgscan = systable_beginscan(tgrel, TriggerRelidNameIndexId, true,
+									NULL, 1, &key);
+		while (HeapTupleIsValid(tuple = systable_getnext(tgscan)))
+		{
+			Form_pg_trigger pg_trigger = (Form_pg_trigger) GETSTRUCT(tuple);
+
+			if (namestrcmp(&(pg_trigger->tgname), trigname) == 0)
+			{
+				tupDesc = RelationGetDescr(tgrel);
+				replaces[Anum_pg_trigger_oid - 1] = false; /* skip updating Oid data */
+				replaces[Anum_pg_trigger_tgrelid - 1] = false;
+				replaces[Anum_pg_trigger_tgname - 1] = false;
+				trigoid = pg_trigger->oid;
+				newtup = heap_modify_tuple(tuple, tupDesc, values, nulls, replaces);
+
+				/* Update tuple in pg_trigger */
+				CatalogTupleUpdate(tgrel, &tuple->t_self, newtup);
+
+				heap_freetuple(newtup);
+				is_update = true;
+				break;
+			}
+		}
+		systable_endscan(tgscan);
+	}
 
-	heap_freetuple(tuple);
 	table_close(tgrel, RowExclusiveLock);
 
 	pfree(DatumGetPointer(values[Anum_pg_trigger_tgname - 1]));
@@ -959,6 +1024,15 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	myself.objectId = trigoid;
 	myself.objectSubId = 0;
 
+	/*
+	 * In case of replace trigger, trigger should no-more dependent on old
+	 * referenced objects. Always remove the old dependencies and then
+	 * register new ones. In that way, even if the old referenced object gets
+	 * dropped, trigger will remain in the database.
+	 */
+	if (is_update)
+		deleteDependencyRecordsFor(myself.classId, myself.objectId, true);
+
 	referenced.classId = ProcedureRelationId;
 	referenced.objectId = funcoid;
 	referenced.objectSubId = 0;
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 8891b1d..5a44533 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -3077,7 +3077,8 @@ domainAddConstraint(Oid domainOid, Oid domainNamespace, Oid baseTypeOid,
 	 * Store the constraint in pg_constraint
 	 */
 	ccoid =
-		CreateConstraintEntry(constr->conname,	/* Constraint Name */
+		CreateConstraintEntry(InvalidOid,
+							  constr->conname,	/* Constraint Name */
 							  domainNamespace,	/* namespace */
 							  CONSTRAINT_CHECK, /* Constraint Type */
 							  false,	/* Is Deferrable */
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 1525c0d..f7e9f58 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -4314,6 +4314,8 @@ _copyCreateTrigStmt(const CreateTrigStmt *from)
 	CreateTrigStmt *newnode = makeNode(CreateTrigStmt);
 
 	COPY_STRING_FIELD(trigname);
+	COPY_SCALAR_FIELD(replace);
+	COPY_SCALAR_FIELD(isconstraint);
 	COPY_NODE_FIELD(relation);
 	COPY_NODE_FIELD(funcname);
 	COPY_NODE_FIELD(args);
@@ -4322,7 +4324,6 @@ _copyCreateTrigStmt(const CreateTrigStmt *from)
 	COPY_SCALAR_FIELD(events);
 	COPY_NODE_FIELD(columns);
 	COPY_NODE_FIELD(whenClause);
-	COPY_SCALAR_FIELD(isconstraint);
 	COPY_NODE_FIELD(transitionRels);
 	COPY_SCALAR_FIELD(deferrable);
 	COPY_SCALAR_FIELD(initdeferred);
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 4f34189..f398597 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -2019,6 +2019,8 @@ static bool
 _equalCreateTrigStmt(const CreateTrigStmt *a, const CreateTrigStmt *b)
 {
 	COMPARE_STRING_FIELD(trigname);
+	COMPARE_SCALAR_FIELD(replace);
+	COMPARE_SCALAR_FIELD(isconstraint);
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_NODE_FIELD(funcname);
 	COMPARE_NODE_FIELD(args);
@@ -2027,7 +2029,6 @@ _equalCreateTrigStmt(const CreateTrigStmt *a, const CreateTrigStmt *b)
 	COMPARE_SCALAR_FIELD(events);
 	COMPARE_NODE_FIELD(columns);
 	COMPARE_NODE_FIELD(whenClause);
-	COMPARE_SCALAR_FIELD(isconstraint);
 	COMPARE_NODE_FIELD(transitionRels);
 	COMPARE_SCALAR_FIELD(deferrable);
 	COMPARE_SCALAR_FIELD(initdeferred);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 1219ac8..5aeffdc 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -5391,48 +5391,50 @@ am_type:
  *****************************************************************************/
 
 CreateTrigStmt:
-			CREATE TRIGGER name TriggerActionTime TriggerEvents ON
+			CREATE opt_or_replace TRIGGER name TriggerActionTime TriggerEvents ON
 			qualified_name TriggerReferencing TriggerForSpec TriggerWhen
 			EXECUTE FUNCTION_or_PROCEDURE func_name '(' TriggerFuncArgs ')'
 				{
 					CreateTrigStmt *n = makeNode(CreateTrigStmt);
-					n->trigname = $3;
-					n->relation = $7;
-					n->funcname = $13;
-					n->args = $15;
-					n->row = $9;
-					n->timing = $4;
-					n->events = intVal(linitial($5));
-					n->columns = (List *) lsecond($5);
-					n->whenClause = $10;
-					n->transitionRels = $8;
+					n->replace = $2;
+					n->trigname = $4;
+					n->relation = $8;
+					n->funcname = $14;
+					n->args = $16;
+					n->row = $10;
+					n->timing = $5;
+					n->events = intVal(linitial($6));
+					n->columns = (List *) lsecond($6);
+					n->whenClause = $11;
+					n->transitionRels = $9;
 					n->isconstraint  = false;
 					n->deferrable	 = false;
 					n->initdeferred  = false;
 					n->constrrel = NULL;
 					$$ = (Node *)n;
 				}
-			| CREATE CONSTRAINT TRIGGER name AFTER TriggerEvents ON
+			| CREATE opt_or_replace CONSTRAINT TRIGGER name AFTER TriggerEvents ON
 			qualified_name OptConstrFromTable ConstraintAttributeSpec
 			FOR EACH ROW TriggerWhen
 			EXECUTE FUNCTION_or_PROCEDURE func_name '(' TriggerFuncArgs ')'
 				{
 					CreateTrigStmt *n = makeNode(CreateTrigStmt);
-					n->trigname = $4;
-					n->relation = $8;
-					n->funcname = $17;
-					n->args = $19;
+					n->replace = $2;
+					n->trigname = $5;
+					n->relation = $9;
+					n->funcname = $18;
+					n->args = $20;
 					n->row = true;
 					n->timing = TRIGGER_TYPE_AFTER;
-					n->events = intVal(linitial($6));
-					n->columns = (List *) lsecond($6);
-					n->whenClause = $14;
+					n->events = intVal(linitial($7));
+					n->columns = (List *) lsecond($7);
+					n->whenClause = $15;
 					n->transitionRels = NIL;
 					n->isconstraint  = true;
-					processCASbits($10, @10, "TRIGGER",
+					processCASbits($11, @11, "TRIGGER",
 								   &n->deferrable, &n->initdeferred, NULL,
 								   NULL, yyscanner);
-					n->constrrel = $9;
+					n->constrrel = $10;
 					$$ = (Node *)n;
 				}
 		;
diff --git a/src/include/catalog/pg_constraint.h b/src/include/catalog/pg_constraint.h
index 9600ece..0d938f1 100644
--- a/src/include/catalog/pg_constraint.h
+++ b/src/include/catalog/pg_constraint.h
@@ -182,7 +182,8 @@ typedef enum ConstraintCategory
 } ConstraintCategory;
 
 
-extern Oid	CreateConstraintEntry(const char *constraintName,
+extern Oid	CreateConstraintEntry(Oid existing_constraint_oid,
+								  const char *constraintName,
 								  Oid constraintNamespace,
 								  char constraintType,
 								  bool isDeferrable,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 518abe4..821e02d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2427,6 +2427,8 @@ typedef struct CreateAmStmt
 typedef struct CreateTrigStmt
 {
 	NodeTag		type;
+	bool		replace;		/* when true, replace trigger if already exists */
+	bool		isconstraint;	/* This is a constraint trigger */
 	char	   *trigname;		/* TRIGGER's name */
 	RangeVar   *relation;		/* relation trigger is on */
 	List	   *funcname;		/* qual. name of function to call */
@@ -2438,7 +2440,6 @@ typedef struct CreateTrigStmt
 	int16		events;			/* "OR" of INSERT/UPDATE/DELETE/TRUNCATE */
 	List	   *columns;		/* column names, or NIL for all columns */
 	Node	   *whenClause;		/* qual expression, or NULL if none */
-	bool		isconstraint;	/* This is a constraint trigger */
 	/* explicitly named transition data */
 	List	   *transitionRels; /* TriggerTransition nodes, or NIL if none */
 	/* The remaining fields are only used for constraint triggers */
diff --git a/src/test/regress/expected/triggers.out b/src/test/regress/expected/triggers.out
index e9da4ef..e9a9551 100644
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -3007,3 +3007,152 @@ create trigger aft_row after insert or update on trigger_parted
 create table trigger_parted_p1 partition of trigger_parted for values in (1)
   partition by list (a);
 create table trigger_parted_p1_1 partition of trigger_parted_p1 for values in (1);
+-- 
+-- Test case for CREATE OR REPLACE TRIGGER
+--
+create table my_table (id integer);
+create function before_replacement() returns trigger as $$
+begin
+raise notice 'function replaced by another function';
+return null;
+end; $$ language plpgsql;
+create function after_replacement() returns trigger as $$
+begin
+raise notice 'function to replace the initial function';
+return null;
+end; $$ language plpgsql;
+create or replace trigger my_trig before insert on my_table for each row execute procedure before_replacement();
+insert into my_table (id) values (1);
+NOTICE:  function replaced by another function
+create or replace trigger my_trig before insert on my_table for each row execute procedure after_replacement();
+insert into my_table (id) values (2);
+NOTICE:  function to replace the initial function
+drop trigger my_trig on my_table;
+drop function before_replacement();
+drop function after_replacement();
+drop table my_table;
+-- setup for another test of CREATE OR REPLACE TRIGGER
+drop table if exists parted_trig;
+NOTICE:  table "parted_trig" does not exist, skipping
+drop trigger if exists my_trig on parted_trig;
+NOTICE:  relation "parted_trig" does not exist, skipping
+drop function if exists before_replacement;
+NOTICE:  function before_replacement() does not exist, skipping
+drop function if exists after_replacement;
+NOTICE:  function after_replacement() does not exist, skipping
+create table parted_trig (a int) partition by range (a);
+create table parted_trig_1 partition of parted_trig for values from (0) to (1000) partition by range (a);
+create table parted_trig_1_1 partition of parted_trig_1 for values from (0) to (100);
+create table parted_trig_2 partition of parted_trig for values from (1000) to (2000);
+create table default_parted_trig partition of parted_trig default;
+create function before_replacement() returns trigger as $$
+begin
+raise notice 'before';
+return null;
+end; $$ language plpgsql;
+create function after_replacement() returns trigger as $$
+begin
+raise notice 'after';
+return null;
+end; $$ language plpgsql;
+-- trigger attached to the parent partition table is replaced by a new one to the parent partition table.
+-- vefify that all partitioned table share the latter trigger in this case.
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  before
+insert into parted_trig_1 (a) values (1);
+NOTICE:  before
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  before
+insert into parted_trig_2 (a) values (1500);
+NOTICE:  before
+insert into parted_trig (a) values (2500);
+NOTICE:  before
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  after
+insert into parted_trig_1 (a) values (1);
+NOTICE:  after
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  after
+insert into parted_trig_2 (a) values (1500);
+NOTICE:  after
+insert into parted_trig (a) values (2500);
+NOTICE:  after
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+-- trigger attached to the parent partition table is replaced by a new one to the child partition table.
+-- verify that only the child partition's trigger is replaced and other tables' triggers aren't.
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  before
+insert into parted_trig_1 (a) values (1);
+NOTICE:  before
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  before
+insert into parted_trig_2 (a) values (1500);
+NOTICE:  before
+insert into parted_trig (a) values (2500);
+NOTICE:  before
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  after
+insert into parted_trig_1 (a) values (1);
+NOTICE:  after
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  after
+insert into parted_trig_2 (a) values (1500);
+NOTICE:  before
+insert into parted_trig (a) values (2500);
+NOTICE:  before
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+-- trigger attached to the child partition table is replaced by a new one to the parent partition table.
+-- verify that the child partition's trigger is replaced by the new one as well and other partition share the same one.
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  before
+insert into parted_trig_1 (a) values (1);
+NOTICE:  before
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  before
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  after
+insert into parted_trig_1 (a) values (1);
+NOTICE:  after
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  after
+insert into parted_trig_2 (a) values (1500);
+NOTICE:  after
+insert into parted_trig (a) values (2500);
+NOTICE:  after
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+-- trigger attached to the child partition table is replaced by a new one to the child partition table.
+-- verify that the trigger of the child parition is replaced and no other partition has the partition.
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  before
+insert into parted_trig_1 (a) values (1);
+NOTICE:  before
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  before
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+NOTICE:  after
+insert into parted_trig_1 (a) values (1);
+NOTICE:  after
+insert into parted_trig_1_1 (a) values (10);
+NOTICE:  after
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+truncate parted_trig;
+drop trigger my_trig on parted_trig_1;
+drop table parted_trig;
+drop function before_replacement;
+drop function after_replacement;
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index 80ffbb4..ceb27c6 100644
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -2274,3 +2274,133 @@ create trigger aft_row after insert or update on trigger_parted
 create table trigger_parted_p1 partition of trigger_parted for values in (1)
   partition by list (a);
 create table trigger_parted_p1_1 partition of trigger_parted_p1 for values in (1);
+
+-- 
+-- Test case for CREATE OR REPLACE TRIGGER
+--
+create table my_table (id integer);
+create function before_replacement() returns trigger as $$
+begin
+raise notice 'function replaced by another function';
+return null;
+end; $$ language plpgsql;
+
+create function after_replacement() returns trigger as $$
+begin
+raise notice 'function to replace the initial function';
+return null;
+end; $$ language plpgsql;
+
+create or replace trigger my_trig before insert on my_table for each row execute procedure before_replacement();
+insert into my_table (id) values (1);
+
+create or replace trigger my_trig before insert on my_table for each row execute procedure after_replacement();
+insert into my_table (id) values (2);
+
+drop trigger my_trig on my_table;
+drop function before_replacement();
+drop function after_replacement();
+drop table my_table;
+
+-- setup for another test of CREATE OR REPLACE TRIGGER
+drop table if exists parted_trig;
+drop trigger if exists my_trig on parted_trig;
+drop function if exists before_replacement;
+drop function if exists after_replacement;
+
+create table parted_trig (a int) partition by range (a);
+create table parted_trig_1 partition of parted_trig for values from (0) to (1000) partition by range (a);
+create table parted_trig_1_1 partition of parted_trig_1 for values from (0) to (100);
+create table parted_trig_2 partition of parted_trig for values from (1000) to (2000);
+create table default_parted_trig partition of parted_trig default;
+
+create function before_replacement() returns trigger as $$
+begin
+raise notice 'before';
+return null;
+end; $$ language plpgsql;
+
+create function after_replacement() returns trigger as $$
+begin
+raise notice 'after';
+return null;
+end; $$ language plpgsql;
+
+-- trigger attached to the parent partition table is replaced by a new one to the parent partition table.
+-- vefify that all partitioned table share the latter trigger in this case.
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+
+-- trigger attached to the parent partition table is replaced by a new one to the child partition table.
+-- verify that only the child partition's trigger is replaced and other tables' triggers aren't.
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+
+-- trigger attached to the child partition table is replaced by a new one to the parent partition table.
+-- verify that the child partition's trigger is replaced by the new one as well and other partition share the same one.
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+create or replace trigger my_trig after insert on parted_trig for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+
+-- trigger attached to the child partition table is replaced by a new one to the child partition table.
+-- verify that the trigger of the child parition is replaced and no other partition has the partition.
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure before_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+create or replace trigger my_trig after insert on parted_trig_1 for each row execute procedure after_replacement();
+insert into parted_trig (a) values (1);
+insert into parted_trig_1 (a) values (1);
+insert into parted_trig_1_1 (a) values (10);
+insert into parted_trig_2 (a) values (1500);
+insert into parted_trig (a) values (2500);
+
+truncate parted_trig;
+drop trigger my_trig on parted_trig_1;
+drop table parted_trig;
+drop function before_replacement;
+drop function after_replacement;