SQL 具有多个条件语法的服务器 CASE 语句

Question

我需要在 select 中添加一个 case 语句，但我似乎无法获得正确的语法，有人可以帮忙吗？

SELECT  
    uuid = pnt.ID
    ,extras = (CASE (SELECT pnt.TypeID as [type], pnt.Source as source)
                  WHEN source = 7 THEN 'a'
                  WHEN source = 1 AND [type] = 0 THEN 'b'
                  WHEN source = 8 THEN 'c'
                  WHEN source = 2 AND [type] = 0 THEN 'd'
                  WHEN source = 3 AND [type] IN (5,6,7,8) THEN 'e'
                  ELSE NULL
                END)
FROM 
    Mydata as pnt

问题多处，selectwithin case不正确，条件source = 7错误，AND组合条件错误，IN条件不正确

我使用 Multiple Criteria In Case Statement 的答案作为案例陈述的基础。

Answer 1

SELECT  
@uuid            = pnt.ID
,@extras         = (CASE WHEN source = 7 THEN
                                'a'
                            WHEN source = 1 AND [type] = 0 THEN
                                'b'
                            WHEN source = 8 THEN
                                'c'
                            WHEN source = 2 AND [type] =0 THEN
                                'd'
                            WHEN source = 3 AND [type] IN  (5,6,7,8) THEN
                                'e'
                            ELSE NULL
                        END
                        )
FROM 
    Mydata as pnt

Answer 2

SELECT ID As uuid, CASE WHEN Source = 7 THEN
'a'
WHEN Source = 1 AND TypeID= 0 THEN
'b'
WHEN Source = 8 THEN
'c'
WHEN Source = 2 AND TypeID= 0 THEN
'd'
WHEN Source = 3 AND TypeID IN (5,6,7,8) THEN
'e'
ELSE
NULL
END 
AS extras FROM Mydata

Answer 3

SELECT
      PNT.ID AS UUID
    , CASE
            WHEN PNT.source = 7 THEN 'a'
            WHEN PNT.source = 1 AND PNT.[type] = 0 THEN 'b'
            WHEN PNT.source = 8 THEN 'c'
            WHEN PNT.source = 2 AND PNT.[type] = 0 THEN 'd'
            WHEN PNT.source = 3 AND PNT.[type] IN (5, 6, 7, 8) THEN 'e'
            ELSE NULL
      END AS EXTRAS
FROM Mydata AS PNT

由于您已经在 table Mydata 中工作，因此 case expression 可以访问 [source] 和 [type] 中保存的值，而无需添加 select.

我已将列别名放在每个列定义的末尾，我相信这比为此目的使用 = 更普遍地得到数据库的支持。

Answer 4

有两种类型的case语句：

一个简单的 case 语句，将一个表达式与一组简单表达式与 return 个特定值进行比较。
将一组布尔表达式计算为 return 个特定值的搜索 case 语句。

https://msdn.microsoft.com/en-us/library/ms144841(v=sql.105).aspx

在您的脚本中您是 "mixing" 他们，因此您的脚本不起作用。这可能是一个很好的解决方案：

SELECT
    pnt.ID
    ,CASE
        WHEN pnt.source = 7 THEN 'a'
        WHEN pnt.source = 1 AND pnt.TypeID = 0 THEN 'b'
        WHEN pnt.source = 8 THEN 'c'
        WHEN pnt.source = 2 AND pnt.TypeID = 0 THEN 'd'
        WHEN pnt.source = 3 AND pnt.TypeID IN (5, 6, 7, 8) THEN 'e'
        ELSE NULL
    END
FROM
    @Mydata AS pnt

警告！如果您需要填充单个变量（uuid、extras），您必须确保您的查询结果只有 1 条记录

SQL 具有多个条件语法的服务器 CASE 语句

SQL Server CASE statement with mupltiple conditionals syntax

sql

sql-server

sql-server-2012