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Subqueries with ALL

语法描述

关键词 ALL 必须跟在比较操作符后面,指如果子查询返回的列中值的 ALL 的比较是 TRUE,则返回 TRUE

operand comparison_operator ALL (subquery)

示例如下:

SELECT s1 FROM t1 WHERE s1 > ALL (SELECT s1 FROM t2);

如上述示例中,假设表 t1 中有一行包含 (10),表 t2 包含 (-5,0,+5),则表达式为 TRUE,因为 10 大于 t2 中的所有三个值。如果表 t2 包含 (12,6,NULL,-100),则表达式为 FALSE,因为在表 t2 中有一个大于 10 的值 12。如果表 t2 包含 (0,NULL,1),则表达式为 NULL

  • 如果表 t2 为空,则表达式为 TRUE。例如,当下表 t2 为空时,表达式是 TRUE
SELECT * FROM t1 WHERE 1 > ALL (SELECT s1 FROM t2);
  • 下面示例中,当表 t2 为空时,这个表达式是 NULL
SELECT * FROM t1 WHERE 1 > (SELECT s1 FROM t2);

或:

SELECT * FROM t1 WHERE 1 > ALL (SELECT MAX(s1) FROM t2);

说明:在书写子查询语法时,要注意考虑到含有 NULL 值的表和空表的情况。

语法结构

> SELECT column_name(s) FROM table_name {WHERE | HAVING} [not] expression comparison_operator ALL (subquery)

示例

create table t1 (a int);
create table t2 (a int, b int);
create table t3 (a int);
create table t4 (a int not null, b int not null);
create table t5 (a int);
create table t6 (a int, b int);
insert into t1 values (2);
insert into t2 values (1,7),(2,7);
insert into t4 values (4,8),(3,8),(5,9);
insert into t5 values (null);
insert into t3 values (6),(7),(3);
insert into t6 values (10,7),(null,7);

mysql> select * from t3 where a <> all (select b from t2);
+------+
| a    |
+------+
|    6 |
|    3 |
+------+
2 rows in set (0.00 sec)

mysql> select * from t4 where 5 > all (select a from t5);
+------+------+
| a    | b    |
+------+------+
|    4 |    8 |
|    3 |    8 |
|    5 |    9 |
+------+------+
3 rows in set (0.01 sec)

mysql> select * from t3 where 10 > all (select b from t2);
+------+
| a    |
+------+
|    6 |
|    7 |
|    3 |
+------+
3 rows in set (0.00 sec)

mysql> select a,b from t6 where a > all ( select a ,b from t4 where a>3);
ERROR 1105 (HY000): subquery should return 1 column