IS

语法说明

IS 运算符用于测试数值是否为布尔值，若是布尔值，则返回结果为 true。其中 boolean_value 可以为 TRUE、FALSE 或 UNKNOWN。

语法结构

  1. > IS boolean_value

示例

  1. mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
  2. +----------+-----------+---------+
  3. | 1 = true | 0 = false | null =  |
  4. +----------+-----------+---------+
  5. | true     | true      | NULL    |
  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<=b and a is not NULL;
  15. +-------+-------+
  16. | a     | b     |
  17. +-------+-------+
  18. | false | true  |
  19. | true  | true  |
  20. | false | false |
  21. +-------+-------+
  22. 3 rows in set (0.01 sec)