“< =>"是什么意思?在MySQL中是什么意思? [英] What does "<=>" in MySQL mean?

问题描述

MySQL中的<=>的含义和作用是什么?

What does <=> in MySQL mean and do?

推荐答案

手册全部说明:

NULL安全等于.这个运算符 执行像这样的相等比较 =运算子，但传回1 如果两个操作数均为NULL，则返回NULL， 如果一个操作数，则返回0而不是NULL 是NULL.

NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.

mysql> select NULL <=> NULL;
+---------------+
| NULL <=> NULL |
+---------------+
|             1 |
+---------------+
1 row in set (0.00 sec)

mysql> select NULL = NULL;
+-------------+
| NULL = NULL |
+-------------+
|        NULL |
+-------------+
1 row in set (0.00 sec)

mysql> select NULL <=> 1;
+------------+
| NULL <=> 1 |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec)

mysql> select NULL = 1;
+----------+
| NULL = 1 |
+----------+
|     NULL |
+----------+
1 row in set (0.00 sec)

mysql> 

这篇关于“< =>"是什么意思?在MySQL中是什么意思?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！