sql-server - 如何与多个 CTE 联合？

Question

如何将 UNION 与多个公共(public)表表达式结合使用？

我正在尝试汇总一些摘要数字，但无论我将 ; 放在哪里，我总是会收到错误

SELECT  COUNT(*)
FROM    dbo.Decision_Data
UNION
SELECT  COUNT(DISTINCT Client_No)
FROM    dbo.Decision_Data
UNION
WITH    [Clients]
          AS ( SELECT   Client_No
               FROM     dbo.Decision_Data
               GROUP BY Client_No
               HAVING   COUNT(*) = 1
             )
    SELECT  COUNT(*) AS [Clients Single Record CTE]
    FROM    Clients;

我很欣赏上面的示例，我可以将单个 CTE 移到开头，但我有许多 CTE，我想UNION

Answer 1

如果您尝试合并多个 CTE，则需要先声明 CTE，然后使用它们:

With Clients As
    (
    Select Client_No
    From dbo.Decision_Data
    Group By Client_No
    Having Count(*) = 1
    )
    , CTE2 As
    (
    Select Client_No
    From dbo.Decision_Data
    Group By Client_No
    Having Count(*) = 2
    )
Select Count(*)
From Decision_Data
Union
Select Count(Distinct Client_No)
From dbo.Decision_Data
Union
Select Count(*)
From Clients
Union
Select Count(*)
From CTE2;

您甚至可以使用一个 CTE 中的另一个:

With Clients As
        (
        Select Client_No
        From dbo.Decision_Data
        Group By Client_No
        Having Count(*) = 1
        )
        , CTE2FromClients As
        (
        Select Client_No
        From Clients
        )
    Select Count(*)
    From Decision_Data
    Union
    Select Count(Distinct Client_No)
    From dbo.Decision_Data
    Union
    Select Count(*)
    From Clients
    Union
    Select Count(*)
    From CTE2FromClients;

WITH common_table_expression (Transact-SQL)