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

  1. > expression IS NULL

示例

  1. mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
  2. +-----------+-----------+--------------+
  3. | 1 is null | 0 is null | null is null |
  4. +-----------+-----------+--------------+
  5. | false     | false     | true         |
  6. +-----------+-----------+--------------+
  7. 1 row in set (0.01 sec)
  1. create table t1 (a boolean,b bool);
  2. insert into t1 values (0,1),(true,false),(true,1),(0,false),(NULL,NULL);
  4. mysql> select * from t1;
  5. +-------+-------+
  6. | a     | b     |
  7. +-------+-------+
  8. | false | true  |
  9. | true  | false |
  10. | true  | true  |
  11. | false | false |
  12. | NULL  | NULL  |
  13. +-------+-------+
  14. mysql> select * from t1 where a IS NULL;
  15. +------+------+
  16. | a    | b    |
  17. +------+------+
  18. | NULL | NULL |
  19. +------+------+
  20. 1 row in set (0.01 sec)