SQL SQL中的无表达式CASE中有多个WHEN？

Multiple WHEN inside no-expression CASE in SQL?

提问by MetaGuru

    DECLARE @TestVal int
SET @TestVal = 5

SELECT
    CASE
        WHEN @TestVal <=3 THEN 'Top 3'
        ELSE 'Other'
    END

I saw this sample code online but I couldn't find an example where there was no expression and it had more than one WHEN, so I am wondering if this type of thing is OK:

我在网上看到了这个示例代码，但是我找不到一个没有表达式并且它有多个 WHEN 的示例，所以我想知道这种类型的东西是否可以：

    DECLARE @TestVal int
SET @TestVal = 5

SELECT
    CASE
        WHEN @TestVal <=3 THEN 'Top 3'
                WHEN (select ...) = 1 THEN 'Other Value'
                WHEN (select ...) = 2 THEN 'Other Value 2'
        ELSE 'Other'
    END

Or do I need to say CASE WHEN for each line?

或者我需要为每一行说 CASE WHEN 吗？

回答by Joel Coehoorn

Yes, that's fine, but I would line up the "WHEN"s vertically and explain it more like this:

是的，那很好，但我会垂直排列“WHEN”并更像这样解释它：

SELECT
    CASE
        WHEN @TestVal <=3  THEN 'Top 3'
        WHEN @TestVal <=10 THEN 'Top 10'
        WHEN @TestVAl <=25 THEN 'Top 25'
        ELSE 'Other'
    END

The formatting might just be a markdown glitch, but the (select...)in your example complicated what should be a simpler snippet.

格式可能只是一个降价小故障，但(select...)在您的示例中，应该是一个更简单的片段。

回答by JoshBerke

Casetakes the following form

案例采用以下形式

CASE WHEN Condition THEN Result
     WHEN Condition2 THEN Result2
ELSE Default
END

Edit

编辑

This assumes your using Microsoft SQL Server other DBMS might be different

这假设您使用 Microsoft SQL Server 其他 DBMS 可能不同

回答by Ken Gee

    SELECT
       CASE
          WHEN @TestVal <=3  THEN 'Top 3'
          WHEN @TestVal <=10 THEN 'Top 10'
          WHEN @TestVAl <=25 THEN 'Top 25'
          ELSE 'Other'
       END

In regards to nesting case statements this can be done as well (up until 10 nested case statements allowed within sql)

关于嵌套 case 语句，也可以这样做（直到 sql 中允许 10 个嵌套 case 语句）

http://msdn.microsoft.com/en-us/library/ms181765.aspx

http://msdn.microsoft.com/en-us/library/ms181765.aspx