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
> IS boolean_value
示例
mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
+-----------+------------+-----------------+
| 1 is true | 0 is false | null is unknown |
+-----------+------------+-----------------+
| true | true | 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<=b and a is not NULL;
+-------+-------+
| a | b |
+-------+-------+
| false | true |
| true | true |
| false | false |
+-------+-------+
3 rows in set (0.01 sec)