IS NULL

语法说明

IS NULL 运算符用于判断列的值是否为空。如果值为空，即为 NULL，则返回 true，否则返回 false。它可以用于 SELECT、INSERT、UPDATE 或 DELETE 语句。

语法结构

> expression IS NULL

示例

mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
+-----------+-----------+--------------+
| 1 is null | 0 is null | null is null |
+-----------+-----------+--------------+
| false     | false     | true         |
+-----------+-----------+--------------+
1 row in set (0.01 sec)

create table t1 (a boolean,b bool);
insert into t1 values (0,1),(true,false),(true,1),(0,false),(NULL,NULL);

mysql> select * from t1;
+-------+-------+
| a     | b     |
+-------+-------+
| false | true  |
| true  | false |
| true  | true  |
| false | false |
| NULL  | NULL  |
+-------+-------+
mysql> select * from t1 where a IS NULL;
+------+------+
| a    | b    |
+------+------+
| NULL | NULL |
+------+------+
1 row in set (0.01 sec)