如何實現加入這個下面的腳本，以避免嵌套的腳本

Question

SELECT UserDCID AS UserDCCompForDelCount1 
FROM CDICentral.dbo.UserDCComponent AS udc 
WHERE(
    UserDCID IN(
     SELECT UserDCID FROM CDICentral.dbo.UserDC AS ud WHERE (
      UserID NOT IN(
       SELECT UserID FROM CVPLocal.dbo.CSWSecurity AS cs 
      ) 
     ) 
    ) 
) 

Answer 1

試試這個sql查詢

SELECT UserDCID AS UserDCCompForDelCount1 
FROM CDICentral.dbo.UserDCComponent AS udc 
INNER JOIN CDICentral.dbo.UserDC AS ud ON udc.UserDCID=ud.UserDCID 
INNER JOIN CVPLocal.dbo.CSWSecurity AS cs ON ud.UserDCID=cs.UserID 

Answer 2

下面是該查詢

SELECT UserDCID AS UserDCCompForDelCount1 FROM CDICentral.dbo.UserDCComponent AS udc 
INNER JOIN (
     SELECT UserDCID FROM CDICentral.dbo.UserDC AS ud 
     EXCEPT 
     SELECT UserID FROM CVPLocal.dbo.CSWSecurity AS cs 
    )Table T 
ON T.UserDCID = udc.UserDCID 

Answer 3

讓我們先從內部查詢：

SELECT UserDCID FROM CDICentral.dbo.UserDC AS ud WHERE (
    UserID NOT IN(
     SELECT UserID FROM CVPLocal.dbo.CSWSecurity AS cs 
    ) 
) 

他們從表中選擇行ud在表cs中沒有匹配，使用字段UserID將它們連接在兩者中。

查詢可以寫成一個LEFT JOIN：

SELECT ud.UserDCID 
FROM CDICentral.dbo.UserDC AS ud 
    LEFT JOIN CVPLocal.dbo.CSWSecurity AS cs 
     ON ud.UserID = cs.UserID  # join the tables on common field `UserID` 
WHERE cs.UserID IS NULL    # the row from `ud` has no match in `cs` 

回到大查詢（我剝奪了高於重構的一部分，因爲停留在道路下面的解釋）：

SELECT UserDCID AS UserDCCompForDelCount1 
FROM CDICentral.dbo.UserDCComponent AS udc 
WHERE(
    UserDCID IN (
     SELECT UserDCID ... 
     ) 
    ) 
) 

當udc和結果集由字段UserDCID（兩者都存在）連接時，此查詢將選擇udc中與內部查詢（刪除的）生成的結果集中的匹配項的行。

這是一個簡單INNER JOIN（讓我們把重構內部查詢後）：

SELECT udc.UserDCID AS UserDCCompForDelCount1 
FROM CDICentral.dbo.UserDCComponent AS udc 
    INNER JOIN CDICentral.dbo.UserDC AS ud 
     ON udc.UserDCID = ud.UserDCID 
    LEFT JOIN CVPLocal.dbo.CSWSecurity AS cs 
     ON ud.UserID = cs.UserID 
WHERE cs.UserID IS NULL 

讓我們讀出新的查詢做什麼：它選擇UserDCComponent S（udc）與UserDC S（ud），唐關聯沒有CSWSecurity（cs）記錄。