Question

我有3个表与多对多关系。我想为此产品选择特定用户和特定产品的最后插入行。

表'user'包含用户的个人信息：

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

表'storage1'包含产品信息：

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

和表活动记录：

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

到目前为止，我有这个代码只会产生与特定用户相关的产品的最大值。

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

结果如下：

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

但我希望得到这个：

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

因为41号鞋子是活动记录表（recordsID 107）中鞋子的最新条目，衬衫尺寸XL是activityRecords表（记录ID 105）中衬衫的最新条目。虽然现在有鞋选择记录ID 106和衬衫选择是记录ID 99.我知道这是相关的，因为我的选择代码（使用max（情况...）），但我不知道如何选择大多数最近进入特定产品和人。有人可以帮我这个吗？谢谢

Answer 1

我建议您继续进行子查询或观看，以便更轻松地获得结果。

Views Syntax Reference

您可以为每个产品创建一个视图，例如：

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';

如果您想为所有用户获取最新的衬衫活动：

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

您可以将此最后一个查询用作新视图或更复杂查询中的子查询。

通过这种方式，您甚至可以获得所有数据的扁平结构（使用您在结果集中预期的所有列）

MySQL选择具有特定条件的行和最后插入的行，用于多个到多个条件

1 个答案: