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MySQL IS和IS NOT运算符有什么用？

2024-05-17 06:22:05 444

在MySQL中， IS和 ISNOT运算符均用于根据布尔值测试值。

IS运算符的语法可以如下-

Val IS Boolean_val

这里瓦尔是我们要反对布尔值测试值。

Boolean_val 是将对其进行测试的布尔值，它可以是TRUE，FALSE或UNKNOWN。

ISNOT 运算符的语法可以如下-

Val IS NOT Boolean_val

这里瓦尔是我们要反对布尔值测试值。

Boolean_val 是将针对其测试val的布尔值，它可以为TRUE，FALSE或UNKNOWN。

以下MySQL语句将演示以上内容-

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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MySQL IS和IS NOT运算符有什么用？

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