TSQL CASE与SELECT语句中的if比较 [英] TSQL CASE with if comparison in SELECT statement

问题描述

我想在SELECT中使用CASE语句.

I would like to use CASE statement in SELECT.

我从用户表中进行选择，并且(作为一个属性)我也使用了嵌套SQL:

I select from user table, and (as one attribute) I also use nested SQL:

SELECT 
   registrationDate, 
   (SELECT COUNT(*) FROM Articles WHERE userId = Users.userId) as articleNumber, 
   hobbies, ...
FROM USERS

然后我想执行一个CASE语句来获取用户的排名(排名取决于articleNumber).

and then I would like to do a CASE statement to get rank of user (rank is dependent on articleNumber).

我尝试过这样:

SELECT 
   registrationDate, 
   (SELECT COUNT(*) FROM Articles WHERE Articles.userId = Users.userId) as articleNumber, 
   ranking =
      CASE
         WHEN articleNumber < 2 THEN 'Ama'
         WHEN articleNumber < 5 THEN 'SemiAma' 
         WHEN articleNumber < 7 THEN 'Good'  
         WHEN articleNumber < 9 THEN 'Better' 
         WHEN articleNumber < 12 THEN 'Best'
         ELSE 'Outstanding'
      END,
   hobbies, etc...
FROM USERS

解析不会显示任何错误，但是当我尝试运行它时会出现错误:

Parsing displays no error, but when I try to run it I get error:

消息207，级别16，状态1，过程GetUserList，行XY
无效的列名"articleNumber".

Msg 207, Level 16, State 1, Procedure GetUserList, Line XY
Invalid column name 'articleNumber'.

我想，CASE无法识别"我的嵌套SELECT.

CASE doesn't "recognize" my nested SELECT, I guess.

我帮助自己解决了其他一些问题，例如 SQL Server 2008-SELECT子句中的Case/If语句 但似乎没有任何作用.

I helped myself with some other solutions like SQL Server 2008 - Case / If statements in SELECT Clause but nothing seems to work.

我也没有发现'<'有任何类似的问题和>"比较.

I also didn't find any similar problem with '<' and '>' comparison.

任何帮助将不胜感激;)

Any help would be greatly appreciated ;)

推荐答案

请在外部选择相同的内容.您无法在同一查询中访问别名.

Please select the same in the outer select. You can't access the alias name in the same query.

SELECT *, (CASE
        WHEN articleNumber < 2 THEN 'Ama'
        WHEN articleNumber < 5 THEN 'SemiAma' 
        WHEN articleNumber < 7 THEN 'Good'  
        WHEN articleNumber < 9 THEN 'Better' 
        WHEN articleNumber < 12 THEN 'Best'
        ELSE 'Outstanding'
        END) AS ranking 
FROM(
    SELECT registrationDate, (SELECT COUNT(*) FROM Articles WHERE Articles.userId = Users.userId) as articleNumber, 
    hobbies, etc...
    FROM USERS
)x

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