Question

我有以下的SQL查询。

declare @RoleID int
SELECT @RoleID = RoleID FROM RoleMaster WHERE RoleEnglishDesc = 'Surveyor'

SELECT * FROM (
 SELECT
  S.ShiftID, 2 AS Flag, ISNULL(U.Latitude, 0) Latitude, ISNULL(U.Longitude, 0) Longitude,
  U.EmployeeEnglishName AS ToolTipEnglish, U.EmployeeArabicName AS ToolTipArabic,
  0 AS CaseStageID, COUNT(C.SurveyorAssigned) AS Assigned
  -- L.EntryTime AS LastEntryTime
  -- S1.cnt AS OnBreak
 FROM 
  Users U
   INNER JOIN dbo.SurveyorShift S ON S.UserId = U.UserID AND S.ShiftStatus = 1
   LEFT JOIN CaseInfoCommandQueue C ON C.SurveyorAssigned = U.UserID
 WHERE U.IsActive = 1
  AND NULLIF(NULLIF(U.Latitude, '0'), '') IS NOT NULL
  AND NULLIF(NULLIF(U.Longitude, '0'), '') IS NOT NULL
  AND ((U.RoleID = @RoleID) OR (U.RoleID2 = @RoleID) OR (U.RoleID3 = @RoleID))
 GROUP BY U.UserID, RoleID, Latitude, Longitude, EmployeeEnglishName, EmployeeArabicName, ShiftID
) D
OUTER APPLY 
(
 SELECT TOP 1 EntryTime FROM DeviceUserLocation DLoc
 WHERE DLoc.ShiftID = D.ShiftID ORDER BY DLoc.EntryTime DESC
) AS L

我在上一个外部的唯一问题是应用于获取输入时间。因为外部施加仅需要10秒。该表DeviceUserLocation也有大量条目。任何克服或步骤以其他方式使用top 1？

Answer 1

为您的数据创建覆盖索引，确保您在每个表上都有聚簇索引，如上所述，如果您不了解聚簇和覆盖索引，请在此处http://en.wikipedia.org/wiki/Database_index#Covering_index，尤其是：{{3您的查询可能正在进行表扫描（搜索或检查每一行）而不是索引查找：在索引中查找值并直接转到该行。（如果该列没有和索引，则无法进行索引查找，如果没有聚簇索引，则无法直接进行索引）

仅针对一个表的SQL查询 - 花费太多时间

1 个答案: