Question

我知道<代码>NUL值与空洞(<>>)值有何区别,但我想通过使用<代码>获得价值。 OR 关键词,我没有获得<代码>NUL的结果。价值

表格一想问:

 titles_and_tags
+----+----------+------+
| id | title    | tag  |
+----+----------+------+
|  1 | title1   | NULL |
|  2 | title2   | tag1 |
|  3 | title3   | tag2 |
|  4 | edit     | NULL |
|  5 | rowdata  | div  |
+----+----------+------+

问题一如上:

select * 
  from `titles_and_tags` 
 WHERE `title` LIKE "title%" 
   AND `tag` = "tag1" OR `tag` IS NULL

因此,我想在这里看到一行(同上,第12段),BUT结果为零。什么是错了?

http://www.ohchr.org。

职业关系,即我的主要问题是:

select * 
  from `titles_and_tags` 
WHERE `title` LIKE "title%" 
AND `tag` = "tag1" OR `tag` LIKE  %

因此,这更像是异地、 s。

Answer 1

提出

select 
  * 
from 
  `titles_and_tags`
WHERE 
  `title` LIKE "title%" AND 
  (`tag` = "tag1" OR `tag` IS NULL)

页: 1 澄清条款,明确将逻辑合起来,确保以你打算的方式执行。

EDIT: In your edit tag like % will match all rows in which tag is not null. Any comparison other than is or not is with a null value is false. I m not sure what you re trying to do with the last query, but I suspect the one that you asked the question with originally is more like what you actually want.

Answer 2

根据你的评论,我的猜测是,你在数据库中插入了 NUL或空座,而不是在上。 2. 确认这项审判:

SELECT * 
FROM titles_and_tags
WHERE tag IN ( NULL ,   )

如果这种情况再次发生,那就会产生问题。

Answer 3

提审(逐字标注)。或者,如果你总结使用背书而不是单一报价。简称表

select * 
  from `titles_and_tags` 
 WHERE title LIKE "title%" 
   AND (tag = "tag1" OR tag IS NULL)

友情链接