# **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**

```text
> expression IS NOT NULL
```

## **示例**

```text
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)
```

```text
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)
```