IS NOT NULL
语法说明
IS NOT NULL
运算符用于判断列的值是否为空。如果值不为空,即不为 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 NOT NULL
示例
mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
+---------------+---------------+------------------+
| 1 is not null | 0 is not null | null is not null |
+---------------+---------------+------------------+
| true | true | false |
+---------------+---------------+------------------+
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 b is NOT NULL;
+-------+-------+
| a | b |
+-------+-------+
| false | true |
| true | false |
| true | true |
| false | false |
+-------+-------+
4 rows in set (0.01 sec)