SQL Server:将几个带有"WITH"部分的SELECT语句组合到一个UNION中

Question

我有几个这样的语句(使用WITH语句):

WITH valDiff AS (SELECT <ComplexClause1> AS v1 FROM [MyTable] WHERE <OtherClause1>) SELECT SUM(CASE WHEN v1 < @MaxVal THEN v1 ELSE @MaxVal END) FROM valDiff

UNION

WITH valDiff AS (SELECT <ComplexClauseN> AS v1 FROM [MyTable] WHERE <OtherClauseN>) SELECT SUM(CASE WHEN v1 < @MaxVal THEN v1 ELSE @MaxVal END) FROM valDiff

我需要将它们合并到一个联合中,以便"一举"返回结果.这些语句本身可以正常工作,但如果我在它们之间添加单词"UNION",就像我上面所示,我得到以下错误:

关键字"UNION"附近的语法不正确.
关键字'with'附近的语法不正确.
如果此语句是公用表表达式,xmlnamespaces子句或更改跟踪上下文子句,则必须以分号结束前一个语句.

我究竟做错了什么？

Answer 1

WITH将跨越UNION中的所有子句

;WITH valDiff AS 
(
whatever
) 
SELECT ... FROM valDiff ...
UNION ALL
SELECT ... FROM valDiff ...

在每个子句中使用不同的CTE(如本例所示):

;WITH CTE1 AS 
(
whatever
) , CTE2 AS
(
something
)
SELECT ... FROM CTE1 ...
UNION ALL
SELECT ... FROM CTE2 ...