【優化SQL Server循環更新、插入耗時長的問題】

一： 工作當中遇到更新較多數據時，使用循環(while,或游標)進行增刪改時，特別費時 

WHILE @i <= @rows
BEGIN
　　SELECT @appNo = AppNumber, @roleid = RoleId, @statusi= Status, @empId = EmployeeId FROM #Atable WHERE ID = @i
　　IF EXISTS(SELECT 1 FROM Btable WHERE AppNumber = @appNo AND RoleID = @roleid AND EmployeeId = @empId)
       BEGIN
      　　UPDATE Btable
　　　　SET Status = @statusi, CreatedBy = NULL, ModifiedOn = GETDATE()
　　　　WHERE AppNumber = @appNoi AND RoleId = @roleidi AND EmployeeId = @empId
　　END
　　ELSE
　　BEGIN
　　　　INSERT INTO Btable(EmployeeId, AppNumber, RoleId, Status, CreatedOn, CreatedBy, ModifiedOn, ModifiedBy)
　　　　SELECT EmployeeId, AppNumber, RoleId, Status, GETDATE(), CreatedBy, GETDATE(), ModifiedBy FROM #Atable WHERE ID = @i
　　END

　　SELECT @i= @i + 1
END

二：利用表左、右連接進行批量刪除解決循環增刪改耗時長的問題

　　update aru set aru.Status = arul.Status, aru.ModifiedOn = GETDATE()
　　from Btable as aru
　　inner join Atable as arul
　　on aru.AppNumber = arul.AppNumber and aru.RoleId = arul.RoleId and aru.EmployeeID = arul.EmployeeID

三：A,B兩張表中有可能數據不相等，可以聲明兩個變量@count1,@count2

　　DECLARE @Count1 int,@Count2 int
　　select @Count1 = COUNT(1) from Atable
　　select @Count2 = COUNT(1) from Btable

四： 根據@count1和@count2的大小判斷是否新增還是刪除

IF(@Count1 > @Count2)
BEGIN　　
　　SELECT * INTO Btable
　　from Atable as arul
　　left join Btable as aru
　　on aru.AppNumber = arul.AppNumber and aru.RoleId = arul.RoleId and aru.EmployeeID = arul.EmployeeID
　　where aru.AppNumber is null and aru.RoleId is null and aru.EmployeeID is null
END
ELSE
BEGIN
　　update aru set aru.Status = 0
　　from Btable as aru
　　left join Atable as arul
　　on aru.AppNumber = arul.AppNumber and aru.RoleId = arul.RoleId and aru.EmployeeID = arul.EmployeeID
　　where arul.AppNumber is null and arul.RoleId is null and arul.EmployeeID is null
END

數據量較多時，又比較、又更新、又新增時，利用循環特別費時，批量更新的效率是循環的幾十倍甚至上百倍

 

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