MySQL的IS和IS NOT運算子有什麼用途？

在MySQL中， IS和 IS NOT運算子都用來將一個值與布林值進行測試。

IS運算子的語法可以如下：

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 lows −

在這裡， Val是我們想要與布林值進行測試的值。

Boolean_val 是要對其進行測試的布林值，它可以是TRUE、FALSE或UNKNOWN。

IS NOT 運算子的語法可以如下所示−

Val IS NOT Boolean_val

在這裡， Val 是我們想要根據布林值進行測試的值。

Boolean_val 是要根據其進行測試的布林值，可以是TRUE、FALSE或UNKNOWN。

以下MySQL語句將示範上述內容−

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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