我可以重複使用一個複雜的條款選擇在哪裏by子句不同的羣體？不同組通過在相同的查詢（選擇/凡）
我在做什麼：
(Select X, Count(*) From [Big where clause with many tables] Group By X)
Union All
(Select Y, Count(*) From [Big where clause with many tables] Group By Y)
我怎樣才能optmise呢？
我使用的是SQL Server 2008中，這將大大函數內部，但可能是一個存儲過程。
WITH basequery AS (Select * From [Big where clause with many tables])
SELECT X, COUNT(*) FROM basequery GROUP BY X
UNION ALL
SELECT Y, COUNT(*) FROM basequery GROUP BY Y;
CTE是爲這樣的情況而製造的。你可以評估（特別是如果有相對較少的x,y組）
一個辦法是給自己物化中間結果爲@table或#temp表，則只是從SELECT（一#temp表會更好，因爲你可以設置比下面的更好指標，它允許填充它被並行化，但這些不具備的功能）
DECLARE @T TABLE
(
X int,
Y int,
Cnt int,
UNIQUE(X,Y,Cnt), /*Cnt just included to make index covering*/
UNIQUE(Y,X,Cnt)
)
INSERT INTO @T
Select X, Y, Count(*)
From [Big where clause with many tables]
Group By X, Y
SELECT X, SUM(Cnt)
FROM @T
GROUP BY X
UNION ALL
SELECT Y, SUM(Cnt)
FROM @T
GROUP BY Y
創建視圖的選擇查詢
CREATE VIEW SomeView
AS
Select X, Y, Count(*) AS C From [Big where clause with many tables]
然後使用視圖：
Select X, C FROM SomeView GROUP BY X
SQL Server 2008中推出了GROUPING SETS()這似乎正是你所追求的。由他人提出的解決方案UNION現在可以輕鬆地與一個單一的選擇來替換GROUPING SETS。
基本上，您使用的是這樣的：
SELECT A, B, C
FROM …
WHERE …
GROUP BY GROUPING SETS ((A), (B), (C))
這相當於
SELECT A, NULL, NULL, …
FROM …
WHERE …
GROUP BY A
UNION ALL
SELECT NULL, B, NULL, …
FROM …
WHERE …
GROUP BY B
UNION ALL
SELECT NULL, NULL, C, …
FROM …
WHERE …
GROUP BY C
所以，您的查詢可能是這樣的：
SELECT X, Y, COUNT(*)
FROM your complex joins and filters
GROUP BY GROUPING SETS ((X), (Y))
或者這樣：
SELECT
CASE WHEN X IS NULL THEN 'Y' ELSE 'X' END AS ObjType
CASE WHEN X IS NULL THEN Y ELSE X END AS Obj,
COUNT(*)
FROM your complex joins and filters
GROUP BY GROUPING SETS ((X), (Y))
第二個假定X不能爲NULL。
參考文獻：
不錯..只是換名/定義:)謝謝 – ariel
@ariel不知道是否「減少昂貴通貨膨脹」你指的是你的問題的代碼或性能？作爲性能優化，這種效應將是中性的。它將重用查詢定義而不是工作。CTE仍會得到兩次評估，該計劃可能與您的原始查詢相同。 –
是的，看到在執行計劃 – ariel