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

8.4 支持根据前述语法进行括号式查询表达式。在最简单的情况下，括号内的查询表达式包含一个 SELECT 或其他返回结果集的语句，且没有后续可选子句：MySQL 8.4 supports parenthesized query expressions according to the preceding syntax. At its simplest, a parenthesized query expression contains a single SELECT or other statement returning a result set and no following optional clauses:

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

TABLE t;

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

括号内的查询表达式也可以包含由一个或多个集合操作链接的查询，例如 UNION，并以任意或全部可选子句结尾：A parenthesized query expression can also contain queries linked by one or more set operations such as UNION, and end with any or all of the optional clauses:

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 在 UNION 和 EXCEPT，因此以下两个语句是等价的：INTERSECT acts before UNION and EXCEPT, so that the following two statements are equivalent:

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);

括号内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能包含括号内的查询表达式：Parenthesized query expressions are also used as query expressions, so a query expression, usually composed of query blocks, may also consist of parenthesized query expressions:

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

查询块可能带有后尾 ORDER BY 和 LIMIT 子句，这些子句在外集操作之前应用，ORDER BY，以及 LIMITQuery blocks may have trailing ORDER BY and LIMIT clauses, which are applied before the outer set operation, ORDER BY, and LIMIT.

你不能让查询块后尾带有 ORDER BY 或 LIMIT 而不用括号包裹，但括号可以以多种方式强制执行：You cannot have a query block with a trailing ORDER BY or LIMIT without wrapping it in parentheses but parentheses may be used for enforcement in various ways:

本节描述的语法受某些限制：The syntax described in this section is subject to certain restrictions: