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)