Don't throw error for DROP DATABASE IF EXISTS

src/backend/distributed/executor/multi_utility.c

@@ -549,11 +549,15 @@ multi_ProcessUtility(PlannedStmt *pstmt,
 	 */
 	if (IsA(parsetree, DropdbStmt))
 	{
+		const bool missingOK = true;
 		DropdbStmt *dropDbStatement = (DropdbStmt *) parsetree;
 		char *dbname = dropDbStatement->dbname;
-		Oid databaseOid = get_database_oid(dbname, false);
+		Oid databaseOid = get_database_oid(dbname, missingOK);
 
-		StopMaintenanceDaemon(databaseOid);
+		if (OidIsValid(databaseOid))
+		{
+			StopMaintenanceDaemon(databaseOid);
+		}
 	}
 
 	/* set user if needed and go ahead and run local utility using standard hook */

src/test/regress/expected/multi_utility_statements.out

@@ -268,3 +268,10 @@ FETCH BACKWARD noHoldCursor;
 COMMIT;
 FETCH ABSOLUTE 5 FROM noHoldCursor;
 ERROR:  cursor "noholdcursor" does not exist
+-- Test we don't throw an error for DROP IF EXISTS
+DROP DATABASE IF EXISTS not_existing_database;
+NOTICE:  database "not_existing_database" does not exist, skipping
+DROP TABLE IF EXISTS not_existing_table;
+NOTICE:  table "not_existing_table" does not exist, skipping
+DROP SCHEMA IF EXISTS not_existing_schema;
+NOTICE:  schema "not_existing_schema" does not exist, skipping

src/test/regress/sql/multi_utility_statements.sql

@@ -146,3 +146,8 @@ FETCH ABSOLUTE 5 FROM noHoldCursor;
 FETCH BACKWARD noHoldCursor;
 COMMIT;
 FETCH ABSOLUTE 5 FROM noHoldCursor;
+
+-- Test we don't throw an error for DROP IF EXISTS
+DROP DATABASE IF EXISTS not_existing_database;
+DROP TABLE IF EXISTS not_existing_table;
+DROP SCHEMA IF EXISTS not_existing_schema;