4 files changed, 32 insertions, 1 deletions
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index e6084203a88..3b89dd009bc 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -122,6 +122,24 @@ DefineSequence(CreateSeqStmt *seq)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("unlogged sequences are not supported")));
 
+	/*
+	 * If if_not_exists was given and a relation with the same name already
+	 * exists, bail out. (Note: we needn't check this when not if_not_exists,
+	 * because DefineRelation will complain anyway.)
+	 */
+	if (seq->if_not_exists)
+	{
+		RangeVarGetAndCheckCreationNamespace(seq->sequence, NoLock, &seqoid);
+		if (OidIsValid(seqoid))
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							seq->sequence->relname)));
+			return InvalidOid;
+		}
+	}
+
 	/* Check and set all option values */
 	init_params(seq->options, true, &new, &owned_by);
 
@@ -210,7 +228,7 @@ DefineSequence(CreateSeqStmt *seq)
 	stmt->options = NIL;
 	stmt->oncommit = ONCOMMIT_NOOP;
 	stmt->tablespacename = NULL;
-	stmt->if_not_exists = false;
+	stmt->if_not_exists = seq->if_not_exists;
 
 	seqoid = DefineRelation(stmt, RELKIND_SEQUENCE, seq->ownerId);
 	Assert(seqoid != InvalidOid);
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index f5ddc1ced7c..aa053a0f158 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -3330,6 +3330,7 @@ _copyCreateSeqStmt(const CreateSeqStmt *from)
 	COPY_NODE_FIELD(sequence);
 	COPY_NODE_FIELD(options);
 	COPY_SCALAR_FIELD(ownerId);
+	COPY_SCALAR_FIELD(if_not_exists);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index ccd6064bf7d..719923e02e7 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1566,6 +1566,7 @@ _equalCreateSeqStmt(const CreateSeqStmt *a, const CreateSeqStmt *b)
 	COMPARE_NODE_FIELD(sequence);
 	COMPARE_NODE_FIELD(options);
 	COMPARE_SCALAR_FIELD(ownerId);
+	COMPARE_SCALAR_FIELD(if_not_exists);
 
 	return true;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 71ce7ee2ddf..6f4d6455df6 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3486,6 +3486,17 @@ CreateSeqStmt:
 					n->sequence = $4;
 					n->options = $5;
 					n->ownerId = InvalidOid;
+					n->if_not_exists = false;
+					$$ = (Node *)n;
+				}
+			| CREATE OptTemp SEQUENCE IF_P NOT EXISTS qualified_name OptSeqOptList
+				{
+					CreateSeqStmt *n = makeNode(CreateSeqStmt);
+					$7->relpersistence = $2;
+					n->sequence = $7;
+					n->options = $8;
+					n->ownerId = InvalidOid;
+					n->if_not_exists = true;
 					$$ = (Node *)n;
 				}
 		;