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優化實例:從運行30分鐘到運行只要30秒

以下的SQL語句在服務器需要運行長達30分鐘才能完成:












SELECT     dbo.ComFlow.ComFlowCode, dbo.ComFlow.ComCode, dbo.ComFlow.CustCode, dbo.ComFlow.DepartCode, dbo.ComFlow.SaleCode,                       dbo.ComFlow.EmpCode, dbo.ComFlow.Quantity * dbo.Commodity.ConvertRate AS Quantity, CONVERT(datetime, DATENAME(yyyy,                       dbo.ComFlow.FlowDate) + '-' + DATENAME(mm, dbo.ComFlow.FlowDate) + '-' + DATENAME(dd, dbo.ComFlow.FlowDate)) AS FlowDate,                       dbo.ComFlow.SalType, dbo.Employee.DepartCode AS DepartIn, dbo.Sale.DepartCode AS DepartOut,                       dbo.ComFlow.Quantity * dbo.Commodity.TradePrice * dbo.Commodity.Discount / 100 AS Total, dbo.Department.GrpCode AS GrpCodeIn,                       Department1.GrpCode AS GrpCodeOutFROM         dbo.ComFlow INNER JOIN                      dbo.Customer ON                 dbo.ComFlow.SalType IN (N'促銷', N'流向退貨', N'多級流向') AND dbo.ComFlow.CustCode = dbo.Customer.CustCode                 Or ComFlow_1.SalType IN (N'自然流向', N'自然流向退貨') AND ComFlow_1.OutCustCode = Customer_1.CustCode            INNER JOIN                      dbo.CustomerRelation ON dbo.ComFlow.ComCode = dbo.CustomerRelation.ComCode AND                       dbo.CustomerRelation.CustCode = dbo.Customer.CustCode INNER JOIN                      dbo.Employee ON dbo.CustomerRelation.EmpCode = dbo.Employee.EmpCode INNER JOIN                      dbo.Sale ON dbo.ComFlow.SaleCode = dbo.Sale.SaleCode INNER JOIN                      dbo.Department ON dbo.Department.DepartCode = dbo.Employee.DepartCode INNER JOIN                      dbo.Department AS Department1 ON Department1.DepartCode = dbo.Sale.DepartCode AND                       dbo.Department.GrpCode <> Department1.GrpCode INNER JOIN                      dbo.Commodity ON dbo.ComFlow.ComCode = dbo.Commodity.ComCodeWHERE     (NOT (dbo.ComFlow.SalType = N'流向退貨')) OR                      (NOT (dbo.Customer.Type = N'醫藥公司'))

雖然說,我們使用這個語句的應用是一個BI應用,實時性要求不高,但是,我覺得沒有道理會運行這么久,應該有辦法優化。

第一步,我看了看索引,好像沒有問題,都有

第二步,檢查關系,有沒有錯,沒有錯,和應用要求是一致的,尤其計算出來的結果和同事使用另外一種方法的計算結果是一致的(同事使用多個視圖分步累加)。

第三步,看看這個語句有沒有什么特別之處?

我注意到特別之處就是使用底色標出的部分:

dbo.ComFlow.SalType IN (N'促銷', N'流向退貨', N'多級流向')AND dbo.ComFlow.CustCode = dbo.Customer.CustCode                 Or ComFlow_1.SalType IN (N'自然流向', N'自然流向退貨') AND ComFlow_1.OutCustCode = Customer_1.CustCode

這是一個Or關系的關聯?就是這個問題?

分析這個語句可以看出,這個Or語句其實是可以分解成Union語句的,所以把它變成下面的:

SELECT     dbo.ComFlow.ComFlowCode, dbo.ComFlow.ComCode, dbo.ComFlow.CustCode, dbo.ComFlow.DepartCode, dbo.ComFlow.SaleCode,                       dbo.ComFlow.EmpCode, dbo.ComFlow.Quantity * dbo.Commodity.ConvertRate AS Quantity, CONVERT(datetime, DATENAME(yyyy,                       dbo.ComFlow.FlowDate) + '-' + DATENAME(mm, dbo.ComFlow.FlowDate) + '-' + DATENAME(dd, dbo.ComFlow.FlowDate)) AS FlowDate,                       dbo.ComFlow.SalType, dbo.Employee.DepartCode AS DepartIn, dbo.Sale.DepartCode AS DepartOut,                       dbo.ComFlow.Quantity * dbo.Commodity.TradePrice * dbo.Commodity.Discount / 100 AS Total, dbo.Department.GrpCode AS GrpCodeIn,                       Department1.GrpCode AS GrpCodeOutFROM         dbo.ComFlow INNER JOIN                      dbo.Customer ON dbo.ComFlow.SalType IN (N'促銷', N'流向退貨', N'多級流向') AND dbo.ComFlow.CustCode = dbo.Customer.CustCode INNER JOIN                      dbo.CustomerRelation ON dbo.ComFlow.ComCode = dbo.CustomerRelation.ComCode AND                       dbo.CustomerRelation.CustCode = dbo.Customer.CustCode INNER JOIN                      dbo.Employee ON dbo.CustomerRelation.EmpCode = dbo.Employee.EmpCode INNER JOIN                      dbo.Sale ON dbo.ComFlow.SaleCode = dbo.Sale.SaleCode INNER JOIN                      dbo.Department ON dbo.Department.DepartCode = dbo.Employee.DepartCode INNER JOIN                      dbo.Department AS Department1 ON Department1.DepartCode = dbo.Sale.DepartCode AND                       dbo.Department.GrpCode <> Department1.GrpCode INNER JOIN                      dbo.Commodity ON dbo.ComFlow.ComCode = dbo.Commodity.ComCodeWHERE     (NOT (dbo.ComFlow.SalType = N'流向退貨')) OR                      (NOT (dbo.Customer.Type = N'醫藥公司'))UNION ALLSELECT     ComFlow_1.ComFlowCode, ComFlow_1.ComCode, ComFlow_1.CustCode, ComFlow_1.DepartCode, ComFlow_1.SaleCode, ComFlow_1.EmpCode,                       ComFlow_1.Quantity * Commodity_1.ConvertRate AS Quantity, CONVERT(datetime, DATENAME(yyyy, ComFlow_1.FlowDate) + '-' + DATENAME(mm,                       ComFlow_1.FlowDate) + '-' + DATENAME(dd, ComFlow_1.FlowDate)) AS FlowDate, ComFlow_1.SalType, Employee_1.DepartCode AS DepartIn,                       Sale_1.DepartCode AS DepartOut, ComFlow_1.Quantity * Commodity_1.TradePrice * Commodity_1.Discount / 100 AS Total,                       Department_1.GrpCode AS GrpCodeIn, Department1.GrpCode AS GrpCodeOutFROM         dbo.ComFlow AS ComFlow_1 INNER JOIN                      dbo.Customer AS Customer_1 ON ComFlow_1.SalType IN (N'自然流向', N'自然流向退貨') AND                       ComFlow_1.OutCustCode = Customer_1.CustCode INNER JOIN                      dbo.CustomerRelation AS CustomerRelation_1 ON ComFlow_1.ComCode = CustomerRelation_1.ComCode AND                       CustomerRelation_1.CustCode = Customer_1.CustCode INNER JOIN                      dbo.Employee AS Employee_1 ON CustomerRelation_1.EmpCode = Employee_1.EmpCode INNER JOIN                      dbo.Sale AS Sale_1 ON ComFlow_1.SaleCode = Sale_1.SaleCode INNER JOIN                      dbo.Department AS Department_1 ON Department_1.DepartCode = Employee_1.DepartCode INNER JOIN                      dbo.Department AS Department1 ON Department1.DepartCode = Sale_1.DepartCode AND Department_1.GrpCode <> Department1.GrpCode INNER JOIN                      dbo.Commodity AS Commodity_1 ON ComFlow_1.ComCode = Commodity_1.ComCodeWHERE     (NOT (ComFlow_1.SalType = N'流向退貨')) OR                      (NOT (Customer_1.Type = N'醫藥公司'))

沒有想到,效果太明顯了,之前需要30分鐘才能運行完畢的語句只要30幾秒就完成了。

這里可以看出,Or的語句可能破壞了索引的作用。使用Or進行關聯雖然邏輯非常清楚,但是效率低。

使用Union雖然冗長,但是用在這里效率要高。

(T114)

作者:http://www.zhujiangroad.com
來源:http://www.zhujiangroad.com
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