| 以下的SQL语句在服务器需要运行长达30分钟才能完成:
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 GrpCodeOut
FROM dbo.ComFlow INNER JOIN
dbo.Customer ON
dbo.ComFlow.SalType IN (N'促销', N'流向退货', N'多级流向') AND dbo.ComFlow.CustCode = dbo.Customer.CustCode
Or ComFlow_1.SalType IN (N'自然流向', N'自然流向退货') 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.ComCode
WHERE (NOT (dbo.ComFlow.SalType = N'流向退货')) OR
(NOT (dbo.Customer.Type = N'医药公司'))
虽然说，我们使用这个语句的应用是一个BI应用，实时性要求不高，但是，我觉得没有道理会运行这么久，应该有办法优化。第一步，我看了看索引，似乎没有问题，都有
第二步，检查关系，有没有错，没有错，和应用要求是一致的，尤其计算出来的结果和同事使用另外一种方法的计算结果是一致的（同事使用多个视图分步累加）。
第三步，看看这个语句有没有什么非凡之处？
我注重到非凡之处就是使用Pink底色标出的部分：
dbo.ComFlow.SalType IN (N'促销', N'流向退货', N'多级流向') AND dbo.ComFlow.CustCode = dbo.Customer.CustCode
Or ComFlow_1.SalType IN (N'自然流向', N'自然流向退货') AND ComFlow_1.OutCustCode = Customer_1.CustCode 这是一个Or关系的关联？就是这个问题？
分析这个语句可以看出，这个Or语句其实是可以分解成Union语句的，所以把它变成下面的： 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,
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