查询"不等于"不起作用

Question

我有这样一个非常简单的查询:

SELECT * FROM `all_conversations` WHERE `deleted_1` != '1';

我的deleted_1默认是null或一些用户ID,但由于某种原因这个查询总是返回我0行,我也试过<>但仍然没有运气什么可能是错的？

EDTI因此在运行更多查询后我发现我的问题是deleted_1字段的默认值,NULL所以我修改了我的查询,现在它工作正常:

SELECT *
FROM `all_conversations`
WHERE `deleted_1` != 'NULL'
AND `deleted_1` != 23

Answer 1

SELECT * FROM all_conversations WHERE deleted_1 <> 1 OR deleted_1 IS NULL

NULL值需要特殊处理:http://dev.mysql.com/doc/refman/5.1/en/working-with-null.html

我建议使用diamond operator(<>),!=因为第一个是有效的SQL,第二个是MySQL的添加.

Answer 2

我建议使用NULL-safe运算符和否定

SELECT * FROM `all_conversations` WHERE NOT(`deleted_1` <=> '1');

Answer 3

你能试试这个吗：deleted_1 is not null and deleted_1 != '1'？

mysql> select 0 is not null and 0 != '1', 1 is not null and 1 != '1', null is not null and null != '1';
+----------------------------+----------------------------+----------------------------------+
| 0 is not null and 0 != '1' | 1 is not null and 1 != '1' | null is not null and null != '1' |
+----------------------------+----------------------------+----------------------------------+
|                          1 |                          0 |                                0 |
+----------------------------+----------------------------+----------------------------------+

或这个deleted_1 is null or deleted_1 != '1'：

mysql> select 0 is null or 0 != '1', 1 is null or 1 != '1', null is null or null != '1';
+-----------------------+-----------------------+-----------------------------+
| 0 is null or 0 != '1' | 1 is null or 1 != '1' | null is null or null != '1' |
+-----------------------+-----------------------+-----------------------------+
|                     1 |                     0 |                           1 |
+-----------------------+-----------------------+-----------------------------+

这实际上取决于您想拿回什么。