DROP TABLE IF EXISTS t1, child1, child2;
CREATE TABLE child1 (a INT PRIMARY KEY);
CREATE TABLE child2 (a INT PRIMARY KEY);
CREATE TABLE t1 (a INT PRIMARY KEY) UNION(child1);
SHOW CREATE TABLE t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `a` int(11) NOT NULL,
  PRIMARY KEY (`a`)
) ENGINE=XENGINE DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci
ALTER TABLE t1 UNION = (child1,child2);
SHOW CREATE TABLE t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `a` int(11) NOT NULL,
  PRIMARY KEY (`a`)
) ENGINE=XENGINE DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci
DROP TABLE t1, child1, child2;