MySQL NULL-safe等于运算符是什么，它与比较运算符有什么不同？

MySQL NULL-safe等于运算符，相当于标准SQL的IS NOT DISTINCT FROM运算符，执行类似于=运算符的等式比较。它的符号是<=>。在我们有两个NULL作为操作数的情况下，它与比较运算符的表现有所不同。请考虑下面的例子，了解NULL-safe运算符及其与比较运算符的区别−

mysql> Select 50 <=> 50, NULL <=> NULL, 100 <=> NULL;
+-----------+---------------+--------------+
| 50 <=> 50 | NULL <=> NULL | 100 <=> NULL |
+-----------+---------------+--------------+
|         1 |             1 |            0 |
+-----------+---------------+--------------+
1 row in set (0.00 sec)

mysql> Select 50 = 50, NULL = NULL, 100 = NULL;
+---------+-------------+------------+
| 50 = 50 | NULL = NULL | 100 = NULL |
+---------+-------------+------------+
|       1 |        NULL |       NULL |
+---------+-------------+------------+
1 row in set (0.00 sec)

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