CREATE_OR_REPLACE_TRIGGER_v12.patch

diff --git a/doc/src/sgml/ref/create_trigger.sgml b/doc/src/sgml/ref/create_trigger.sgml
index 60346e1..2e508db 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 ] ]
@@ -48,14 +48,22 @@ CREATE [ CONSTRAINT ] TRIGGER <replaceable class="parameter">name</replaceable>
   <title>Description</title>
 
   <para>
-   <command>CREATE TRIGGER</command> creates a new trigger.  The
-   trigger will be associated with the specified table, view, or foreign table
+   <command>CREATE TRIGGER</command> creates a new trigger.
+   <command>CREATE OR REPLACE TRIGGER</command> will either create a
+   new trigger, or replace an existing trigger. The trigger will be
+   associated with the specified table, view, or foreign table
    and will execute the specified
    function <replaceable class="parameter">function_name</replaceable> when
    certain operations are performed on that table.
   </para>
 
   <para>
+   To replace the current definition of an existing trigger, use
+   <command>CREATE OR REPLACE TRIGGER</command>, by specifying the same
+   trigger's name and the corresponding table's name where the trigger belongs.
+  </para>
+
+  <para>
    The trigger can be specified to fire before the
    operation is attempted on a row (before constraints are checked and
    the <command>INSERT</command>, <command>UPDATE</command>, or
@@ -446,6 +454,14 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
   </para>
 
   <para>
+   When replacing an existing trigger with <command>CREATE OR REPLACE
+   TRIGGER</command>, there are restrictions. You cannot replace triggers with
+   a different type of trigger. That means it is impossible to replace a regular
+   trigger with a constraint trigger, and vice versa. Also, in a transaction
+   you cannot replace triggers that are already fired and have pending events.
+  </para>
+
+  <para>
    A column-specific trigger (one defined using the <literal>UPDATE OF
    <replaceable>column_name</replaceable></literal> syntax) will fire when any
    of its columns are listed as targets in the <command>UPDATE</command>
diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 67144aa..1a52fa3 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2434,7 +2434,8 @@ 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 0974f3e..5ccebb9 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1862,7 +1862,8 @@ index_constraint_create(Relation heapRelation,
 	/*
 	 * Construct a pg_constraint entry.
 	 */
-	conOid = CreateConstraintEntry(constraintName,
+	conOid = CreateConstraintEntry(InvalidOid,
+								   constraintName,
 								   namespaceId,
 								   constraintType,
 								   deferrable,
@@ -1927,6 +1928,8 @@ 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";
@@ -1938,7 +1941,6 @@ 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 0d70cb0..3f35e50 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
+ * "existing_constraint_oid" if that is other than InvalidOid)
  */
 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];
@@ -165,9 +167,12 @@ 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 (!OidIsValid(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);
@@ -221,9 +226,57 @@ 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))
+	{
+		/*
+		 * Replace the existing constraint entry.
+		 */
+		SysScanDesc conscan;
+		ScanKeyData skey[2];
+		HeapTuple	tuple;
+		bool		replaces[Natts_pg_constraint];
+		Form_pg_constraint constrForm;
+
+		ScanKeyInit(&skey[0],
+					Anum_pg_constraint_oid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(existing_constraint_oid));
+
+		conscan = systable_beginscan(conDesc,
+									 ConstraintOidIndexId,
+									 true,
+									 NULL,
+									 1,
+									 skey);
 
-	CatalogTupleInsert(conDesc, tup);
+		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);
+
+		/* 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);
+	}
 
 	ObjectAddressSet(conobject, ConstraintRelationId, conOid);
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index e0ac4e0..a2a1c4d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8832,7 +8832,8 @@ 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,
@@ -9100,7 +9101,8 @@ addFkRecurseReferencing(List **wqueue, Constraint *fkconstraint, Relation rel,
 			else
 				conname = fkconstraint->conname;
 			constrOid =
-				CreateConstraintEntry(conname,
+				CreateConstraintEntry(InvalidOid,
+									  conname,
 									  RelationGetNamespace(partition),
 									  CONSTRAINT_FOREIGN,
 									  fkconstraint->deferrable,
@@ -9502,7 +9504,8 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
 
 		indexOid = constrForm->conindid;
 		constrOid =
-			CreateConstraintEntry(fkconstraint->conname,
+			CreateConstraintEntry(InvalidOid,
+								  fkconstraint->conname,
 								  constrForm->connamespace,
 								  CONSTRAINT_FOREIGN,
 								  fkconstraint->deferrable,
@@ -10513,6 +10516,8 @@ 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;
@@ -10533,7 +10538,6 @@ 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;
@@ -10562,6 +10566,8 @@ 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;
@@ -10570,7 +10576,6 @@ 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)
 	{
@@ -10618,6 +10623,8 @@ 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;
@@ -10626,7 +10633,6 @@ 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 672fccf..49ca88f 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 +185,10 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	char	   *oldtablename = NULL;
 	char	   *newtablename = NULL;
 	bool		partition_recurse;
+	bool		is_update = false;
+	Oid			existing_constraint_oid = InvalidOid;
+	bool		trigger_exists = false;
+	bool		internal_trigger = false;
 
 	if (OidIsValid(relOid))
 		rel = table_open(relOid, ShareRowExclusiveLock);
@@ -668,6 +673,86 @@ 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;
+				internal_trigger = pg_trigger->tgisinternal;
+				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)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("trigger \"%s\" for relation \"%s\" already exists",
+							stmt->trigname, RelationGetRelationName(rel))));
+		else
+		{
+			/*
+			 * An internal trigger cannot be replaced by another user defined
+			 * trigger. This should exclude the case that internal trigger is
+			 * child trigger of partition table and needs to be rewritten when
+			 * the parent trigger is replaced by user.
+			 */
+			if (internal_trigger && isInternal == false && in_partition == false)
+				ereport(ERROR,
+						(errcode(ERRCODE_DUPLICATE_OBJECT),
+						 errmsg("trigger \"%s\" for relation \"%s\" is an internal trigger",
+								stmt->trigname, RelationGetRelationName(rel))));
+
+			/*
+			 * CREATE OR REPLACE CONSTRAINT TRIGGER command can't replace
+			 * non-constraint trigger.
+			 */
+			if (stmt->isconstraint && !OidIsValid(existing_constraint_oid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DUPLICATE_OBJECT),
+						 errmsg("trigger \"%s\" for relation \"%s\" is a regular trigger",
+								stmt->trigname, RelationGetRelationName(rel)),
+						 errhint("use CREATE OR REPLACE TRIGGER to replace a regular trigger")));
+
+			/*
+			 * CREATE OR REPLACE TRIGGER command can't replace constraint
+			 * trigger.
+			 */
+			if (!stmt->isconstraint && OidIsValid(existing_constraint_oid))
+				ereport(ERROR,
+						(errcode(ERRCODE_DUPLICATE_OBJECT),
+						 errmsg("trigger \"%s\" for relation \"%s\" is a constraint trigger",
+								stmt->trigname, RelationGetRelationName(rel)),
+						 errhint("use CREATE OR REPLACE CONSTRAINT TRIGGER to replace a constraint trigger")));
+		}
+	}
+
 	/*
 	 * Find and validate the trigger function.
 	 */
@@ -695,7 +780,8 @@ 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 +813,6 @@ 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 +830,6 @@ 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 +957,56 @@ 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
+	{
+		HeapTuple	newtup;
+		TupleDesc	tupDesc;
+		bool		replaces[Natts_pg_trigger];
+
+		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 +1049,15 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	myself.objectId = trigoid;
 	myself.objectSubId = 0;
 
+	/*
+	 * In order to replace trigger, trigger should not be dependent on old
+	 * referenced objects. Remove the old dependencies and then register new
+	 * ones. In this case, while 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 483bb65..8e25349 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -3100,7 +3100,8 @@ 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 0409a40..d90c0bf 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -4315,6 +4315,8 @@ _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);
@@ -4323,7 +4325,6 @@ _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 e2d1b98..6e261db 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -2020,6 +2020,8 @@ 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);
@@ -2028,7 +2030,6 @@ _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 0d101d8..ef9fe03 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -5211,48 +5211,50 @@ 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 60c2f45..346412e 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2429,6 +2429,9 @@ 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 */
@@ -2440,7 +2443,6 @@ 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 5e76b3a..537403a 100644
--- a/src/test/regress/expected/triggers.out
+++ b/src/test/regress/expected/triggers.out
@@ -3052,3 +3052,155 @@ 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 funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create or replace trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcA();
+insert into my_table (id) values (1);
+NOTICE:  hello from funcA
+create or replace trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcB();
+insert into my_table (id) values (2);
+NOTICE:  hello from funcB
+drop trigger my_trig on my_table;
+drop function funcA();
+drop function funcB();
+drop table my_table;
+-- test trigger can't be replaced without OR REPLACE clause
+create table my_table (id integer);
+create function funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcA();
+create trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcB(); -- should fail
+ERROR:  trigger "my_trig" for relation "my_table" already exists
+drop trigger my_trig on my_table;
+create constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcA();
+create constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+ERROR:  trigger "my_trig" for relation "my_table" already exists
+drop trigger my_trig on my_table;
+drop function funcA();
+drop function funcB();
+drop table my_table;
+-- test for detecting incompatible replacement of trigger
+create table my_table (id integer);
+create function funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create or replace trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcA();
+create or replace constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+ERROR:  trigger "my_trig" for relation "my_table" is a regular trigger
+HINT:  use CREATE OR REPLACE TRIGGER to replace a regular trigger
+drop trigger my_trig on my_table;
+create or replace constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB();
+create or replace trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+ERROR:  trigger "my_trig" for relation "my_table" is a constraint trigger
+HINT:  use CREATE OR REPLACE CONSTRAINT TRIGGER to replace a constraint trigger
+drop table my_table;
+drop function funcA();
+drop function funcB();
+-- test CREATE OR REPLACE TRIGGER on partition table
+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 funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+-- test that trigger can be replaced by another one
+-- at the same level of partition table
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcA
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcB();
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcB
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+-- test that child trigger cannot be replaced directly
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcA
+create or replace trigger my_trig
+  after insert on parted_trig_1
+  for each row execute procedure funcB(); -- should fail
+ERROR:  trigger "my_trig" for relation "parted_trig_1" is an internal trigger
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcA
+drop trigger my_trig on parted_trig;
+-- test that trigger is overwritten by another one
+-- defined by upper level
+create or replace trigger my_trig
+  after insert on parted_trig_1
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcA
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcB();
+insert into parted_trig (a) values (50);
+NOTICE:  hello from funcB
+drop trigger my_trig on parted_trig;
+-- cleanup
+drop table parted_trig;
+drop function funcA();
+drop function funcB();
diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql
index e228d0a..fc8da77 100644
--- a/src/test/regress/sql/triggers.sql
+++ b/src/test/regress/sql/triggers.sql
@@ -2295,3 +2295,148 @@ 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 funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create or replace trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcA();
+insert into my_table (id) values (1);
+create or replace trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcB();
+insert into my_table (id) values (2);
+drop trigger my_trig on my_table;
+drop function funcA();
+drop function funcB();
+drop table my_table;
+
+-- test trigger can't be replaced without OR REPLACE clause
+create table my_table (id integer);
+create function funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcA();
+create trigger my_trig
+  before insert on my_table
+  for each row execute procedure funcB(); -- should fail
+drop trigger my_trig on my_table;
+create constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcA();
+create constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+drop trigger my_trig on my_table;
+drop function funcA();
+drop function funcB();
+drop table my_table;
+
+-- test for detecting incompatible replacement of trigger
+create table my_table (id integer);
+create function funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+create or replace trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcA();
+create or replace constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+drop trigger my_trig on my_table;
+create or replace constraint trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB();
+create or replace trigger my_trig
+  after insert on my_table
+  for each row execute procedure funcB(); -- should fail
+drop table my_table;
+drop function funcA();
+drop function funcB();
+
+-- test CREATE OR REPLACE TRIGGER on partition table
+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 funcA() returns trigger as $$
+begin
+  raise notice 'hello from funcA';
+  return null;
+end; $$ language plpgsql;
+create function funcB() returns trigger as $$
+begin
+  raise notice 'hello from funcB';
+  return null;
+end; $$ language plpgsql;
+
+-- test that trigger can be replaced by another one
+-- at the same level of partition table
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcB();
+insert into parted_trig (a) values (50);
+truncate parted_trig;
+drop trigger my_trig on parted_trig;
+
+-- test that child trigger cannot be replaced directly
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+create or replace trigger my_trig
+  after insert on parted_trig_1
+  for each row execute procedure funcB(); -- should fail
+insert into parted_trig (a) values (50);
+drop trigger my_trig on parted_trig;
+
+-- test that trigger is overwritten by another one
+-- defined by upper level
+create or replace trigger my_trig
+  after insert on parted_trig_1
+  for each row execute procedure funcA();
+insert into parted_trig (a) values (50);
+create or replace trigger my_trig
+  after insert on parted_trig
+  for each row execute procedure funcB();
+insert into parted_trig (a) values (50);
+drop trigger my_trig on parted_trig;
+
+-- cleanup
+drop table parted_trig;
+drop function funcA();
+drop function funcB();