Question

我的查询非常简单：

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

我的deleted_1默认为null或某个用户ID，但由于某种原因，此查询总是返回0行，我也尝试<>但仍然没有运气可能是什么错？

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，它是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

我建议使用菱形运算符（<>）支持!=，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：deleted_1 is not null and deleted_1 != '1'吗？

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 |
+-----------------------+-----------------------+-----------------------------+

这实际上取决于你想要回来的东西。

Answer 4

试试这个..希望它会对你有用

SELECT *
FROM `all_conversations`
WHERE `deleted_1` IS NOT NULL
AND `deleted_1` <> 23

Answer 5

我同意以上答案，如果您有多个AND条件，只需添加其他详细信息像下面的查询一样，您应该将要检查的列与Where条件的第一部分不等于或为null，因为OR部分会使您的条件不正确

  SELECT ts.*, ct.Name AS CategoryName
FROM MJ.Tasks  AS ts 
LEFT JOIN MJ.Lookup_Category AS ct ON ts.CategoryID = ct.ID
WHERE ts.Status!=1 OR ts.Status IS NULL AND ts.CategoryID = @CategoryID AND ts.UserID = @UserID AND  CAST(ts.EndDate AS DATE) = CAST(@EndDate AS DATE)

Answer 6

如何删除1？

周围的单引号

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

查询“不等于”不起作用

6 个答案: