5 files changed, 55 insertions, 0 deletions

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 5712fe19c5c..5aa9bbb19c1 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -1376,6 +1376,7 @@ CreateExtension(CreateExtensionStmt *stmt)
 			csstmt->schemaname = schemaName;
 			csstmt->authid = NULL;		/* will be created by current user */
 			csstmt->schemaElts = NIL;
+			csstmt->if_not_exists = false;
 			CreateSchemaCommand(csstmt, NULL);
 
 			/*
diff --git a/src/backend/commands/schemacmds.c b/src/backend/commands/schemacmds.c
index cd5ce06ca76..e69c86bbabf 100644
--- a/src/backend/commands/schemacmds.c
+++ b/src/backend/commands/schemacmds.c
@@ -84,6 +84,23 @@ CreateSchemaCommand(CreateSchemaStmt *stmt, const char *queryString)
 		   errdetail("The prefix \"pg_\" is reserved for system schemas.")));
 
 	/*
+	 * If if_not_exists was given and the schema already exists, bail out.
+	 * (Note: we needn't check this when not if_not_exists, because
+	 * NamespaceCreate will complain anyway.)  We could do this before making
+	 * the permissions checks, but since CREATE TABLE IF NOT EXISTS makes its
+	 * creation-permission check first, we do likewise.
+	 */
+	if (stmt->if_not_exists &&
+		SearchSysCacheExists1(NAMESPACENAME, PointerGetDatum(schemaName)))
+	{
+		ereport(NOTICE,
+				(errcode(ERRCODE_DUPLICATE_SCHEMA),
+				 errmsg("schema \"%s\" already exists, skipping",
+						schemaName)));
+		return;
+	}
+
+	/*
 	 * If the requested authorization is different from the current user,
 	 * temporarily set the current user so that the object(s) will be created
 	 * with the correct ownership.
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 84ab16d61f1..9387ee90c9f 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -3613,6 +3613,7 @@ _copyCreateSchemaStmt(const CreateSchemaStmt *from)
 	COPY_STRING_FIELD(schemaname);
 	COPY_STRING_FIELD(authid);
 	COPY_NODE_FIELD(schemaElts);
+	COPY_SCALAR_FIELD(if_not_exists);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index e537e43809c..226b99a1d27 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1909,6 +1909,7 @@ _equalCreateSchemaStmt(const CreateSchemaStmt *a, const CreateSchemaStmt *b)
 	COMPARE_STRING_FIELD(schemaname);
 	COMPARE_STRING_FIELD(authid);
 	COMPARE_NODE_FIELD(schemaElts);
+	COMPARE_SCALAR_FIELD(if_not_exists);
 
 	return true;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 62ff9178286..7feadeac169 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -1169,6 +1169,7 @@ CreateSchemaStmt:
 						n->schemaname = $5;
 					n->authid = $5;
 					n->schemaElts = $6;
+					n->if_not_exists = false;
 					$$ = (Node *)n;
 				}
 			| CREATE SCHEMA ColId OptSchemaEltList
@@ -1178,6 +1179,40 @@ CreateSchemaStmt:
 					n->schemaname = $3;
 					n->authid = NULL;
 					n->schemaElts = $4;
+					n->if_not_exists = false;
+					$$ = (Node *)n;
+				}
+			| CREATE SCHEMA IF_P NOT EXISTS OptSchemaName AUTHORIZATION RoleId OptSchemaEltList
+				{
+					CreateSchemaStmt *n = makeNode(CreateSchemaStmt);
+					/* One can omit the schema name or the authorization id. */
+					if ($6 != NULL)
+						n->schemaname = $6;
+					else
+						n->schemaname = $8;
+					n->authid = $8;
+					if ($9 != NIL)
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("CREATE SCHEMA IF NOT EXISTS cannot include schema elements"),
+								 parser_errposition(@9)));
+					n->schemaElts = $9;
+					n->if_not_exists = true;
+					$$ = (Node *)n;
+				}
+			| CREATE SCHEMA IF_P NOT EXISTS ColId OptSchemaEltList
+				{
+					CreateSchemaStmt *n = makeNode(CreateSchemaStmt);
+					/* ...but not both */
+					n->schemaname = $6;
+					n->authid = NULL;
+					if ($7 != NIL)
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("CREATE SCHEMA IF NOT EXISTS cannot include schema elements"),
+								 parser_errposition(@7)));
+					n->schemaElts = $7;
+					n->if_not_exists = true;
 					$$ = (Node *)n;
 				}
 		;