mysql - 如何根据条件获取最后修改的行

Question

我有下面提到的表格:

Table1:

ID        Unique_Key      Date                     MapId
II-10     RTE-011         2018-04-07 15:18:25      er-12-tt
II-11     RTE-011         2018-05-17 11:44:47      er-13-td
II-12     RTE-011         2018-06-12 13:22:29      ee-13-rt
II-13     RTE-012         2018-04-07 19:17:14      eg-15-st
II-14     RTE-012         2018-04-07 21:22:37      hr-15-yt
II-15     RTE-013         2018-07-07 20:27:38      tr-16-yt
II-15     RTE-013         2018-08-07 14:18:33      tr-16-yt

Table2: 

Id              Status
er-12-tt        Open
er-13-td        Closed
er-13-rt        Closed
eg-15-st        Closed
hr-15-yt        Pending
tr-16-yt        Open
tr-16-yt        Pending

通过使用上面提到的两个表，我想仅获取状态为已关闭的记录的最新行。

我们需要排除那些任何值不等于Closed的Unique_Key

所需的输出为:

ID        Unique_Key      Date                     MapId          Id         Status
II-12     RTE-011         2018-06-12 13:22:29      ee-13-rt       er-13-rt        Closed
II-13     RTE-012         2018-04-07 19:17:14      eg-15-st       eg-15-st        Closed    

Answer 1

首先，在子查询中，我们确定一组 Unique_Key 的最大日期。我们过滤掉那些 Unique_Key至少有一行包含 Status = Closed 的值，使用HAVING SUM(t2.Status = Closed) > 0

该子查询的结果集随后被用作 Derived Table 。然后将其连接回 Table1和Table2 ，我们过滤掉那些最大状态为 Closed 的情况，使用WHERE t22.Status = 'Closed'

尝试:

SELECT t11.ID, 
       t11.Unique_Key, 
       t11.Date, 
       t11.MapId, 
       t22.Id, 
       t22.Status 
FROM Table1 AS t11 
JOIN Table2 AS t22 ON t22.Id = t11.MapId 
JOIN (
       SELECT t1.Unique_Key, 
              MAX(t1.Date) AS max_Date 
       FROM Table1 AS t1 
       JOIN Table2 AS t2 ON t2.Id = t1.MapId 
       GROUP BY t1.Unique_Key 
       HAVING SUM(t2.Status = Closed) > 0 
     ) AS dt ON dt.Unique_Key = t11.Unique_Key AND 
                dt.max_Date = t11.Date 
WHERE t22.Status = 'Closed'