T-SQL查詢出現意外的性能問題

Question

我有以下T-SQL查詢：

SELECT Wk.WeekID,
       Wk.WeekStart,
       SUM(CASE WHEN NOT(Task.WeekDate IS NULL) THEN 1 ELSE 0 END) AS WeekCount,
       SUM(CASE WHEN NOT(Task.DayDate IS NULL) THEN 1 ELSE 0 END) AS DayCount
FROM tblPerWeek AS Wk
LEFT OUTER JOIN tblPerTask AS Task ON (Task.WeekDate = Wk.WeekStart) 
                                   OR (Task.DayDate BETWEEN Wk.WeekStart AND Wk.WeekEnd)
WHERE (Wk.WeekStart <= @DateEnd) AND (Wk.WeekEnd >= @DateStart)
GROUP BY Wk.WeekID, Wk.WeekStart

tblPerWeek表的結構：

WeekID int
WeekStart date
WeekEnd date

tblPerTask表的結構：

TaskID int
WeekDate date
DayDate date

基本上，查詢計算分配給周（任務WeekCount ）或特定的星期（內DayCount ）。

tblPerWeek有大約2800條記錄， tblPerTask有大約70000條記錄。

現在， (Task.DayDate BETWEEN Wk.WeekStart AND Wk.WeekEnd)條件存在一些問題/故障：

• 如果沒有加入此條件，查詢將立即完成
• 在這種情況下，查詢運行大約需要12秒

有什么收獲？ 關於如何使此查詢更快的任何解決方案？

Answer 1

通常，通過使用UNION查詢來解決使用OR的問題。 如果兩組記錄將互斥，請使用UNION ALL，這甚至更快。

SELECT Wk.WeekID,
       Wk.WeekStart,
       SUM(CASE WHEN NOT(Task.WeekDate IS NULL) THEN 1 ELSE 0 END) AS WeekCount,
       SUM(CASE WHEN NOT(Task.DayDate IS NULL) THEN 1 ELSE 0 END) AS DayCount
FROM tblPerWeek AS Wk
LEFT OUTER JOIN tblPerTask AS Task ON Task.WeekDate = Wk.WeekStart
WHERE (Wk.WeekStart <= @DateEnd) AND (Wk.WeekEnd >= @DateStart)
GROUP BY Wk.WeekID, Wk.WeekStart
UNION 
SELECT Wk.WeekID,
       Wk.WeekStart,
       SUM(CASE WHEN NOT(Task.WeekDate IS NULL) THEN 1 ELSE 0 END) AS WeekCount,
       SUM(CASE WHEN NOT(Task.DayDate IS NULL) THEN 1 ELSE 0 END) AS DayCount
FROM tblPerWeek AS Wk
LEFT OUTER JOIN tblPerTask AS Task ON Task.DayDate BETWEEN Wk.WeekStart AND Wk.WeekEnd
WHERE (Wk.WeekStart <= @DateEnd) AND (Wk.WeekEnd >= @DateStart)
GROUP BY Wk.WeekID, Wk.WeekStart

Answer 2

優化器討厭OR

SELECT Wk.WeekID,
       Wk.WeekStart,
       SUM(CASE WHEN TaskW.WeekDate IS NULL THEN 0 ELSE 1 END) AS WeekCount,
       SUM(CASE WHEN TaskD.DayDate  IS NULL THEN 0 ELSE 1 END) AS DayCount
FROM tblPerWeek AS Wk
LEFT OUTER JOIN tblPerTask AS TaskW ON TaskW.WeekDate = Wk.WeekStart                                       
LEFT OUTER JOIN tblPerTask AS TaskD ON TaskD.DayDate BETWEEN Wk.WeekStart AND Wk.WeekEnd
WHERE Wk.WeekStart <= @DateEnd AND Wk.WeekEnd >= @DateStart
GROUP BY Wk.WeekID, Wk.WeekStart

我想你可以做一個計數，因為null為零

SELECT Wk.WeekID, Wk.WeekStart,
       COUNT(TaskW.WeekDate) AS WeekCount,
       COUNT(TaskD.DayDate)  AS DayCount
FROM tblPerWeek AS Wk
LEFT OUTER JOIN tblPerTask AS TaskW ON TaskW.WeekDate = Wk.WeekStart                                       
LEFT OUTER JOIN tblPerTask AS TaskD ON TaskD.DayDate BETWEEN Wk.WeekStart AND Wk.WeekEnd
WHERE Wk.WeekStart <= @DateEnd AND Wk.WeekEnd >= @DateStart
GROUP BY Wk.WeekID, Wk.WeekStart