"IS DISTINCT FROM"是真正的MySQL运算符吗? [英] Is 'IS DISTINCT FROM' a real MySQL operator?

问题描述

在一本书中，我看到了这种语法:

In one book I see this syntax:

SELECT * FROM inw WHERE id IS DISTINCT FROM 4;

但是我得到一个错误:

错误1064(42000):您的SQL语法有错误；查看与您的MySQL服务器版本相对应的手册以获取正确的语法，以在第1行的"DISTINCT FROM 4"附近使用

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

它可以替代:

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

'IS DISTINCT FROM'是真正的MySQL操作员吗?

Is 'IS DISTINCT FROM' a real MySQL operator?

推荐答案

is distinct from在SQL:2003标准中定义，并且是用于比较两个值的null安全运算符.

is distinct from is defined in the SQL:2003 standard and is a null-safe operator to compare two values.

MySQL支持空安全等于"运算符:<=>.如果否定，您将获得相同的行为. (<=>对应于is not distinct from)

MySQL supports a "null safe equals" operator: <=>. If that is negated, you get the same behaviour. (the <=> corresponds to is not distinct from)

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

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

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

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