Question

我有这个查询，我需要从3个表中提取数据，但是有一些分组需要发生。我知道子查询很糟糕，但我似乎无法以任何其他方式完成此操作。当有数十万行时，这将会崩溃。也许我过于复杂了？我尝试了“分区依据”，但是这会从ERT1中拉回所有行，这会弄乱计数。我不能使用一个组，因为如果我在ERT1上分组，它会搞乱ER1。

我在加入的字段中使用FK和索引。

有人对此有任何想法吗？

非常感谢!!

SELECT ER.EventRegistrationID, DC.DiscountCodeID, DC.DiscountAmount, DC.DiscountCode, DC.ActiveFlag,

    ISNULL((SELECT COUNT(ER1.EventRegistrationID) 
        FROM T_EventRegistration ER1 
        WHERE ER1.DiscountCode = DC.DiscountCode
        AND ER1.EventID = DC.EventID
        AND ER1.OrderCompleteFlag = 1),0) AS NumTimesUsed, --includes refunded orders

    ISNULL((SELECT COUNT(ERT1.TicketNumber) 
        FROM T_EventRegistrationTickets ERT1, T_EventRegistration ER1 
        WHERE ER1.EventRegistrationID = ERT1.EventRegistrationID 
        AND ER1.DiscountCode = DC.DiscountCode
        AND ER1.EventID = DC.EventID
        AND ER1.OrderCompleteFlag = 1
        ),0) AS NumTicketsSold --excludes refunded tickets

FROM T_DiscountCodes DC, T_EventRegistration ER
WHERE DC.DiscountCode *= ER.DiscountCode
AND DC.EventID = 20188
AND DC.DeleteFlag = 0
AND DC.HiddenFlag = 0
AND ER.OrderCompleteFlag = 1
ORDER BY DC.DiscountCode, NumTimesUsed

Answer 1

您可以使用APPLY或创建派生表

来完成此操作

SELECT ER.EventRegistrationID
     , DC.DiscountCodeID
     , DC.DiscountAmount
     , DC.DiscountCode
     , DC.ActiveFlag
     , ISNULL(a,NumTimesUsed,0)
     , ISNULL(a2.NumTicketsSold,0)
FROM T_DiscountCodes DC, T_EventRegistration ER
OUTER APPLY (SELECT COUNT(ERT1.TicketNumber) NumTimesUsed
        FROM T_EventRegistrationTickets ERT1, T_EventRegistration ER1 
        WHERE ER1.EventRegistrationID = ERT1.EventRegistrationID 
        AND ER1.DiscountCode = DC.DiscountCode
        AND ER1.EventID = DC.EventID
        AND ER1.OrderCompleteFlag = 1) a
OUTER APPLY (SELECT COUNT(ER1.EventRegistrationID) NumTicketsSold
        FROM T_EventRegistration ER1 
        WHERE ER1.DiscountCode = DC.DiscountCode
        AND ER1.EventID = DC.EventID
        AND ER1.OrderCompleteFlag = 1) a2
WHERE DC.DiscountCode *= ER.DiscountCode
AND DC.EventID = 20188
AND DC.DeleteFlag = 0
AND DC.HiddenFlag = 0
AND ER.OrderCompleteFlag = 1
ORDER BY DC.DiscountCode, NumTimesUsed

从Select Statement中删除子查询？

1 个答案: