mysql> select * from test_main;
+----+-------+
| id | value |
+----+-------+
| 1 | ONE |
| 2 | TWO |
| 3 | THREE |
+----+-------+
3 rows in set (0.00 sec)
mysql> create table test_main2 select * from test_main;
Query OK, 3 rows affected (0.04 sec)
Records: 3 Duplicates: 0 Warnings: 0
-- 创建视图， sql 语句加了括号， 报错。
CREATE VIEW view_test_main
AS
(
SELECT * FROM test_main
UNION ALL
SELECT * FROM test_main2
);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'UNION
ALL
SELECT * FROM test_main2
)' at line 5
-- 创建视图， sql 语句不加括号， 通过。
mysql> CREATE VIEW view_test_main
-> AS
-> SELECT * FROM test_main
-> UNION ALL
-> SELECT * FROM test_main2;
Query OK, 0 rows affected (0.01 sec)
