mysql - 'IS DISTINCT FROM' 是真正的 MySQL 运算符吗？

Question

在一本书中我看到了这样的语法:

SELECT * FROM inw WHERE id IS DISTINCT FROM 4;

但是我得到一个错误:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DISTINCT FROM 4' at line 1

它是一个替代品:

mysql> SELECT * FROM inw WHERE id is null OR id <> 4;
+------+
| id   |
+------+
| NULL |
| NULL |
|    3 |
+------+

'IS DISTINCT FROM' 是真正的 MySQL 运算符吗？

Answer 1

is distinct from是在 SQL:2003 标准中定义的，是用于比较两个值的 null 安全运算符。

MySQL 支持 "null safe equals" operator: <=> .如果否定，你会得到相同的行为。 (<=>对应于is not distinct from)

SELECT * 
FROM inw 
WHERE not id <=> 4;

SQLFiddle:http://sqlfiddle.com/#!2/0abf2a/3