MySQL的IS和IS NOT运算符有什么用途？

IS操作符的语法可以如下所示：

Val IS Boolean_val

Here Val is the value that we want to test against Boolean value.

Boolean_val is the Boolean value against which the value would be tested and it can be TRUE, FALSE or UNKNOWN.

The syntax of IS NOT operator can be as follows −

在这里， Val是我们想要与布尔值进行测试的值。

Boolean_val 是要对其进行测试的布尔值，它可以是TRUE、FALSE或UNKNOWN。

IS NOT 运算符的语法可以如下所示−

Val IS NOT Boolean_val

在这里， Val 是我们想要根据布尔值进行测试的值。

Boolean_val 是要根据其进行测试的布尔值，可以是TRUE、FALSE或UNKNOWN。

以下MySQL语句将演示上述内容−

mysql> Select 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
+-----------+------------+-----------------+
| 1 IS TRUE | 0 IS FALSE | NULL IS UNKNOWN |
+-----------+------------+-----------------+
|         1 |          1 |               1 |
+-----------+------------+-----------------+
1 row in set (0.00 sec)

mysql> Select 1 IS NOT TRUE, 0 IS NOT FALSE, NULL IS NOT UNKNOWN;
+---------------+----------------+---------------------+
| 1 IS NOT TRUE | 0 IS NOT FALSE | NULL IS NOT UNKNOWN |
+---------------+----------------+---------------------+
|             0 |              0 |                   0 |
+---------------+----------------+---------------------+
1 row in set (0.00 sec)

mysql> Select 0 IS NOT TRUE, 1 IS NOT FALSE, NULL IS NOT UNKNOWN;
+---------------+----------------+---------------------+
| 0 IS NOT TRUE | 1 IS NOT FALSE | NULL IS NOT UNKNOWN |
+---------------+----------------+---------------------+
|             1 |              1 |                   0 |
+---------------+----------------+---------------------+
1 row in set (0.00 sec)

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