MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
parenthesized_query_expression
: (query_expression
[order_by_clause
] [limit_clause
] ) [order_by_clause
] [limit_clause
] [into_clause
]query_expression
:query_block
[UNIONquery_block
[UNIONquery_block
...]] [order_by_clause
] [limit_clause
] [into_clause
]query_block
: SELECT ... (see Section 13.2.10, “SELECT Statement”)order_by_clause
: ORDER BY as for SELECT (see Section 13.2.10, “SELECT Statement”)limit_clause
: LIMIT as for SELECT (see Section 13.2.10, “SELECT Statement”)into_clause
: INTO as for SELECT (see Section 13.2.10, “SELECT Statement”)
MySQL 8.0.22 and higher supports parenthesized query expressions
according to the preceding syntax. At its simplest, a
parenthesized query expression contains a single
SELECT
and no following optional
clauses:
(SELECT 1); (SELECT * FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'mysql');
A parenthesized query expression can also contain a
UNION
comprising multiple
SELECT
statements, 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 | +------+
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:
(SELECT * FROM t1 ORDER BY a) UNION (SELECT * FROM t2 ORDER BY b) ORDER BY z;
Query blocks may have trailing ORDER BY
and
LIMIT
clauses, which are applied before the
outer UNION
and ORDER BY
and LIMIT
.
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:
To enforce LIMIT
on each query block:
(SELECT 1 LIMIT 1) UNION (SELECT 2 LIMIT 1);
To enforce LIMIT
on both query blocks and
the entire query expression:
(SELECT 1 LIMIT 1) UNION (SELECT 2 LIMIT 1) LIMIT 1;
To enforce LIMIT
on the entire query
expression (with no parentheses):
SELECT 1 UNION SELECT 2 LIMIT 1;
Hybrid enforcement: LIMIT
on the first
query block and on the entire query expression:
(SELECT 1 LIMIT 1) UNION SELECT 2 LIMIT 1;
The syntax described in this section is subject to certain restrictions:
If ORDER BY
occurs within a parenthesized
query expression and also is applied in the outer query, the
results are undefined and may change in a future version of
MySQL. The same is true if LIMIT
occurs
within a parenthesized query expression and also is applied
in the outer query.
A trailing INTO
clause for a query
expression is not permitted if there is another
INTO
clause inside parentheses.
Parenthesized query expressions do not permit multiple
levels of ORDER BY
or
LIMIT
operations. For example:
mysql> (SELECT 'a' UNION SELECT 'b' LIMIT 1) LIMIT 2;
ERROR 1235 (42000): This version of MySQL doesn't yet support 'parenthesized
query expression with more than one external level of ORDER/LIMIT operations'