# **IS**

## **Grammar Description**

The `IS` operator is used to test whether the value is a Boolean value. If it is a Boolean value, the result is `true`. where `boolean_value` can be `TRUE`, `FALSE` or `UNKNOWN`.

## **Grammar Structure**

```text
> IS boolean_value
```

## **Example**

```text
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)
```

```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 a<=b and a is not NULL;
+--------+--------+
| a | b |
+--------+--------+
| false | true |
| true | true |
| false | false |
+--------+--------+
3 rows in set (0.01 sec)
```