在SELECT语句中使用if比较的T-SQL CASE

Question

我想在SELECT语句中使用CASE语句。

我从用户表中进行选择，并且（作为一个属性）我还使用嵌套SQL：

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

然后我想要做一个CASE语句来获取用户的等级（等级取决于文章数量）。

我尝试了这样：

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

解析没有错误，但是当我尝试运行它时出现错误：

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

我猜CASE语句不“识别”我的嵌套SELECT。

我已经尝试了一些其他的解决方案，比如SQL Server 2008 - Case / If statements in SELECT Clause，但是似乎都不起作用。

我也没有找到任何类似于“<”和“>”比较的问题。

非常感谢您的任何帮助；）

- CyberHawk

Answer 1

请在外部选择相同的内容。您无法在同一查询中访问别名。

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

- TechDo

Answer 2

应该是：

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

- Justin

Answer 3

你可以尝试以下代码：

WITH CTE_A As (SELECT COUNT(*) as articleNumber,A.UserID  as UserID FROM Articles A
           Inner Join Users U
           on  A.userId = U.userId 
           Group By A.userId , U.userId   ),

B as (Select us.registrationDate,

      CASE
         WHEN CTE_A.articleNumber < 2 THEN 'Ama'
         WHEN CTE_A.articleNumber < 5 THEN 'SemiAma' 
         WHEN CTE_A.articleNumber < 7 THEN 'Good'  
         WHEN CTE_A.articleNumber < 9 THEN 'Better' 
         WHEN CTE_A.articleNumber < 12 THEN 'Best'
         ELSE 'Outstanding'
         END as Ranking,
         us.hobbies, etc...
         FROM USERS Us Inner Join CTE_A 
         on CTE_A.UserID=us.UserID)

Select * from B

- Dia Agha

---

为什么，如果我已经有更简洁的解决方案了。感谢你的努力，但我看不出有什么意义。没有groupBy和其他开销... - CyberHawk