本文介绍了返回空值IN子句mysql的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
在数据库中找不到数据时找不到打印.例如,在我的数据库中,我没有56443
,因此它应该显示'not found'
Print not found when there is no data found in database. For example in my database I do not have 56443
therefore it should print 'not found'
SELECT uid, (CASE WHEN (u.uid = null) THEN 'not found' ELSE 'found' END) as result
FROM (SELECT uid
FROM users
WHERE uid IN (1,2,56443,3)) as u;
获得结果如下
+--------+--------+
| uid | result|
+--------+--------+
| 1 | found |
| 2 | found |
| 3 | found |
+--------+--------+
我也希望not found
行与56443
推荐答案
您需要使用其他方法.您将需要使用UNION ALL创建一个包含所有值的内联视图,然后将其与users表保持连接:
You need to use a different approach. You will need to create a inline view with all the values using the UNION ALL, and then left join it with the users table:
查询1 :
SELECT a.uid, (CASE WHEN (u.uid is null) THEN 'not found' ELSE 'found' END) as result
FROM (select 1 as UID FROM dual
UNION ALL
select 2 as UID FROM dual
UNION ALL
select 56443 as UID FROM dual
UNION ALL
select 3 as UID FROM dual) as a
LEFT JOIN users u on a.uid = u.uid
[结果] :
| UID | result |
|-------|-----------|
| 1 | found |
| 2 | found |
| 3 | found |
| 56443 | not found |
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