sql - 如何在 CTE (SQL Server 2005) 之后使用 if 语句

Question

昨晚我在写一个像这样的简单的T-SQL程序

DECLARE @ROLEID AS INT

SELECT @ROLEID = [ROLE ID] FROM TBLROLE

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
IF (@ROLEID  = 1) 
BEGIN
      //SOMECODE
END
ELSE IF(@ROLEID  = 2) 
BEGIN
      //SOMECODE
END
ELSE
BEGIN 
      //SOMECODE
END

我在编译后发现它会抛出类似“if 附近语句不正确”之类的错误

怎么了？

但是，我通过使用其他方式做到了这一点。但我想知道为什么它不起作用！

Answer 1

公用表表达式在单个语句的上下文中定义：

WITH cte_name AS (
  <cte definition>)
<statement that uses cte>;

因此，您可以执行以下操作：

WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
SELECT * FROM CTE;

或者

WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
UPDATE CTE 
SET somefield = somevalue
WHERE id = somekey;

CTE 后面必须跟一个引用部分或全部 CTE 列的 SELECT、INSERT、UPDATE、MERGE 或 DELETE 语句。CTE 也可以在 CREATE VIEW 语句中指定为视图的定义 SELECT 语句的一部分

Answer 2

您将得到的最接近的是使用 UNION ALL 进行粗略的切换选择：

DECLARE @ROLEID AS INT

SELECT @ROLEID = [ROLE ID] FROM TBLROLE

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 1
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 2
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = 3
...
UNION ALL
SELECT
    --somecolumns
FROM
    CTE
    --other stuff too
WHERE
    @ROLEID = n

Answer 3

有点晚了，但我不能是唯一遇到这个的人。

一个解决方案可能是创建一个像这样的临时表：

-- If previous run of this query fails, the temp table will be deleted.
-- Selecting into creates the temp table which fails if it already exists
IF EXISTS(SELECT [name] FROM tempdb.sys.tables WHERE [name] like '#dtBalansOpgesteldGefilterd%') BEGIN
   DROP TABLE #temp
END;

;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)

-- Followed by select statement as required
SELECT *
INTO #temp
FROM CTE

IF @awsome = 1
BEGIN
    SELECT 'WHATEVERYOUWANT' AS WhateverColumnNameYouWant, *
    FROM #temp
END

Answer 4

尝试将 CTE 放在 IF 中。它对我有用。

IF @awsome = 1
BEGIN
;WITH CTE
AS
( 
    SELECT * FROM SOMETABLE
)
    SELECT 'WHATEVERYOUWANT' FROM CTE
END
ELSE IF @awesome = 2
BEGIN
;WITH CTE2
AS
( 
    SELECT * FROM SOMETABLE
)
    SELECT 'WHATEVERYOUWANT' FROM CTE2
END