MySQL選擇具有特定條件的行，最後一行插入的條件爲多對多

Question

我有3個具有多對多關係的表。我想爲特定用戶和特定產品選擇該產品的最後插入行。

表 '用戶' 包含用戶的個人信息：

userID  persID  firstName  lastName  gender 
42   9559000 Jane   Rae   female 
43   9559001 John   Doe   male 
. 
. 
. 

表 '存放1' 包含產品信息：

storageID  product  productAttribute  productSize  storageQTY 
1    shirt  red     S    10 
2    shirt  blue     M    10 
. 
. 
. 
13   shirt  green    L    10 
14   shirt  green    XL    9 
15   shirt  green    XXL    7 
. 
. 
39   trousers male     60    10 
40   trousers male     62    8 
. 
. 
59   shoes  standard    41    10 
60   shoes  standard    42    7 
61   shoes  standard    43    10 
62   shoes  standard    44    10 
63   shoes  standard    45    9 
. 
. 
72   jacket  red     L    10 
73   jacket  red     XL    9 
74   jacket  red     XXL    6 

和表activityRecords：

recordsID  userID  storageID  startDate  expDate 
99   43   15   2017-09-14 
100   43   74   2017-09-14 
101   43   39   2017-09-14 
102   43   13   2017-09-14 
103   43   14   2017-09-14 
104   43   40   2017-09-14 
105   43   14   2017-09-14 
106   43   63   2017-09-14 
107   43   59   2017-09-14 

到目前爲止，我只有產生與特定用戶有關的產品的最大值的代碼。

select 
     persID, 
     firstName, 
     lastName, 
     gender, 
     max(case when storage1.product = 'shoes' then storage1.productSize end) shoes, 
     max(case when storage1.product = 'trousers' then storage1.productSize end) trousers, 
     max(case when storage1.product = 'shirt' then storage1.productSize end) shirt, 
     max(case when storage1.product = 'shirt' then storage1.productAttribute end) color, 
     max(case when storage1.product = 'jacket' then storage1.productSize end) jacket, 
     startDate, 
     expDate 
    from activityRecords 
     left join user on activityRecords.userID = user.userID 
     left join storage1 on activityRecords.storageID = storage1.storageID 
    where persID='9559001' 
    group by persID, firstName, lastName, gender, startDate, expDate 
    order by persID 

這導致這樣的：

persID  firstName  lastName  gender  shoes  trousers  shirt  color  jacket  startDate  expDate 
9559001 John   Doe   male  45  null   null  null  null  2017-09-14 
9559001 John   Doe   male  null  62   null  null  null  2017-09-14 
9559001 John   Doe   male  null  null   XXL  green  null  2017-09-14 
9559001 John   Doe   male  null  null   null  null  XXL  2017-09-14 

，但我想這一點：

persID  firstName  lastName  gender  shoes  trousers  shirt  color  jacket  startDate  expDate 
9559001 John   Doe   male  41  null   null  null  null  2017-09-14 
9559001 John   Doe   male  null  62   null  null  null  2017-09-14 
9559001 John   Doe   male  null  null   XL  green  null  2017-09-14 
9559001 John   Doe   male  null  null   null  null  XXL  2017-09-14 

因爲鞋號41是鞋activityRecords表的最新條目（recordsID 107） shirt size XL是activityRecords表中襯衫的最新條目（recordsID 105）。 雖然現在有鞋子選擇記錄ID 106和襯衫選擇記錄ID 99.我知道這是相關的，因爲我的選擇代碼（使用max（case when ...）），但我不知道如何選擇特定產品和人員的最新條目。任何人都可以幫助我呢？謝謝

Answer 1

我建議你繼續子查詢或視圖，以便更容易地得到你的結果。

Views Syntax Reference

您可以爲每個產品如一個觀點：如果你想獲得最新的襯衫活動所有用戶

create view shirt_activity_view 
as select 
    ar.userID, 
    ar.recordsID, 
    s1.productSize as shirt, 
    s1.productAttribute as color, 
    ar.startDate, 
    ar.expDate 
from activityRecords as ar 
    inner join storage1 as s1 
    on ar.storageID = s1.storageID 
    and s1.product = 'shirt'; 

：

select 
    * 
from shirt_activity_view 
inner join (
    select 
     userID, 
     max(startDate) as max_start_date 
    from shirt_activity_view 
    group by userID 
) as max_dates 
    on shirt_activity_view.userID = max_dates.userID 
and shirt_activity_view.startDate = max_dates.max_start_date 

你可以使用最後一個查詢作爲新視圖或作爲更復雜查詢中的子查詢。

通過這種方式，你甚至可以讓您的所有數據（使用你在結果集中期待列）