MySQL的IS和IS NOT运算符有什么用途？-tutorial mysql-php.cn

MySQL的IS和IS NOT运算符有什么用途？

在MySQL中，IS和IS NOT操作符都用于将一个值与布尔值进行测试。

IS操作符的语法可以如下所示：

Val IS Boolean_val

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HereValis the value that we want to test against Boolean value.

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

The syntax ofIS NOToperator 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

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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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