parenthesized_query_expression:
    ( query_expression [order_by_clause] [limit_clause] )
      [order_by_clause]
      [limit_clause]
      [into_clause]

query_expression:
    query_block [set_op query_block [set_op query_block ...]]
      [order_by_clause]
      [limit_clause]
      [into_clause]

query_block:
    SELECT ... | TABLE | VALUES

order_by_clause:
    ORDER BY as for SELECT

limit_clause:
    LIMIT as for SELECT

into_clause:
    INTO as for SELECT

set_op:
    UNION | INTERSECT | EXCEPT

MySQL 9.0 根据前面的语法支持带括号的查询表达式。最简单地说，带括号的查询表达式包含一个返回结果集的 SELECT 语句或其他语句，并且后面没有可选子句

(SELECT 1);
(SELECT * FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'mysql');

TABLE t;

VALUES ROW(2, 3, 4), ROW(1, -2, 3);

带括号的查询表达式还可以包含由一个或多个集合操作（例如 UNION）链接的查询，并以任何或所有可选子句结尾

mysql> (SELECT 1 AS result UNION SELECT 2);
+--------+
| result |
+--------+
|      1 |
|      2 |
+--------+
mysql> (SELECT 1 AS result UNION SELECT 2) LIMIT 1;
+--------+
| result |
+--------+
|      1 |
+--------+
mysql> (SELECT 1 AS result UNION SELECT 2) LIMIT 1 OFFSET 1;
+--------+
| result |
+--------+
|      2 |
+--------+
mysql> (SELECT 1 AS result UNION SELECT 2)
       ORDER BY result DESC LIMIT 1;
+--------+
| result |
+--------+
|      2 |
+--------+
mysql> (SELECT 1 AS result UNION SELECT 2)
       ORDER BY result DESC LIMIT 1 OFFSET 1;
+--------+
| result |
+--------+
|      1 |
+--------+
mysql> (SELECT 1 AS result UNION SELECT 3 UNION SELECT 2)
       ORDER BY result LIMIT 1 OFFSET 1 INTO @var;
mysql> SELECT @var;
+------+
| @var |
+------+
|    2 |
+------+

INTERSECT 的优先级高于 UNION 和 EXCEPT，因此以下两个语句是等效的

SELECT a FROM t1 EXCEPT SELECT b FROM t2 INTERSECT SELECT c FROM t3;

SELECT a FROM t1 EXCEPT (SELECT b FROM t2 INTERSECT SELECT c FROM t3);

带括号的查询表达式也用作查询表达式，因此通常由查询块组成的查询表达式也可以由带括号的查询表达式组成

(TABLE t1 ORDER BY a) UNION (TABLE t2 ORDER BY b) ORDER BY z;

查询块可以具有尾随的 ORDER BY 和 LIMIT 子句，这些子句在外部集合操作、ORDER BY 和 LIMIT 之前应用。

您不能在不将查询块括在括号中的情况下使用尾随的 ORDER BY 或 LIMIT，但可以使用括号以各种方式强制执行

本节描述的语法受某些限制