Question

问题：

让我说我有3个公用表格CTE1，CTE2，CTE3。它们都包含MonthID，YearID，ProductID，StoreID，Amount

我有表Years＆amp; Months和YearID＆amp; MonthID是他们的主键。

我需要创建一个报告，其中包含给定时间段内的所有数据，因此我执行以下操作：

SELECT MonthID, YearID, ProductID, StoreID, Amount
FROM Years 
CROSS JOIN Months
CROSS JOIN Products
INNER JOIN Store on Store.StoreId = Products.ProductId
LEFT JOIN CTE1 On CTE1.MonthID = Months.MonthID AND CTE1.YearID = Years AND (CTE1.ProductID = Products.ProductId OR CTE.StoreID = Store.StoreID)
LEFT JOIN CTE2 On CTE2.MonthID = Months.MonthID AND CTE2.YearID = Years AND CTE2.ProductID = Products.ProductId AND CTE2.StoreID = Store.StoreID
LEFT JOIN CTE3 On CTE3.MonthID = Months.MonthID AND CTE3.YearID = Years AND CTE3.ProductID = Products.ProductId AND CTE3.StoreID = Store.StoreID
WHERE CTE1.Amount IS NOT NULL OR CTE2.Amount IS NOT NULL OR CTE3 IS NOT NULL

事情在CTE1列StoreID中，ProductID可以是NULL。也许ProductId，也许StoreId，可能两列都是NULL。

我仍然需要将这些值放在我的报告中....所以我该怎么做？

Answer 1

考虑使用连接条件对CTE1值进行coalesce。这种方式当CTE1.value为null时;该值将替换为联接另一侧的值。最终结果是当CTE1值为null时，它基本上计算为1 = 1语句，并且不会消除任何记录。

当您使用可能否定索引使用的函数时，授予的性能将是次优的。

SELECT MonthID, YearID, ProductID, StoreID, Amount
FROM Years 
CROSS JOIN Months
CROSS JOIN Products
INNER JOIN Store on Store.StoreId = Products.ProductId
LEFT JOIN CTE1 
  ON CTE1.MonthID = Months.MonthID 
 AND CTE1.YearID = Years 
 AND coalesce(CTE1.ProductID, Products.ProductId) = Products.ProductId 
 AND coalesce(CTE1.StoreID, Store.StoreID) = Store.StoreID
LEFT JOIN CTE2 
  On CTE2.MonthID = Months.MonthID 
 AND CTE2.YearID = Years 
 AND CTE2.ProductID = Products.ProductId 
 AND CTE2.StoreID = Store.StoreID
LEFT JOIN CTE3 
  On CTE3.MonthID = Months.MonthID 
 AND CTE3.YearID = Years 
 AND CTE3.ProductID = Products.ProductId 
 AND CTE3.StoreID = Store.StoreID
WHERE CTE1.Amount IS NOT NULL 
   OR CTE2.Amount IS NOT NULL 
   OR CTE3 IS NOT NULL

使用CROSS LEFT JOINS的复杂SQL查询

1 个答案: