SQL select inside select 使用日期时间列作为参考

Question

我有一个 table 看起来像下面的那个：

╔═══════════╦═════════╦═════════════╦═══════════════╦═════════════════════╦═════════════════════╗
║ id_object ║ Name    ║ Activity    ║ Object_Prefix ║ Start_DateTime      ║ End_DateTime        ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 213       ║ Junior  ║ Fixing      ║ G35           ║ 06-11-2020 09:35:06 ║ 06-11-2020 16:39:34 ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 213       ║ Junior  ║ End_turn    ║               ║ 06-11-2020 17:01:25 ║                     ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 213       ║ Richard ║ Auxiliating ║ G35           ║ 06-11-2020 09:35:06 ║ 06-11-2020 16:39:34 ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 213       ║ Richard ║ End_turn    ║               ║ 06-11-2020 17:04:07 ║                     ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 456       ║ Philip  ║ Fixing      ║ G08           ║ 02-11-2020 13:35:09 ║ 02:11:2020 21:58:59 ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 456       ║ Philip  ║ End_turn    ║               ║ 02-11-2020 22:37:51 ║                     ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 102       ║ Julia   ║ Auxiliating ║ N901          ║ 31-10-2020 20:01:30 ║ 01-11-2020 08:09:41 ║
╠═══════════╬═════════╬═════════════╬═══════════════╬═════════════════════╬═════════════════════╣
║ 102       ║ Julia   ║ End_turn    ║               ║ 01-11-2020 08:13:45 ║                     ║
╚═══════════╩═════════╩═════════════╩═══════════════╩═════════════════════╩═════════════════════╝

我一直在尝试 select 将 End turn Times 作为一个新专栏，尽管到目前为止我尝试但没有成功的是：

 select  
  t1.id,
  t1.name,
  t1.activity,
  DATE_FORMAT( t1.Start_DateTime, "%d/%m-%Y %H:%i:%s") as Start,
  (Select DATE_FORMAT(t1.Start_DateTime, "%d/%m-%Y %H:%i:%s")
    from Activities t2 
     WHERE t2.Activities = "End_turn" AND t2.id_object = t1.id_object) as end_activity
  FROM 
   Activities t1 
 WHERE 
 t1.Object_Prefix != ""
GROUP BY
t.Start_DateTime

我期待的结果是这样的：

但是 end_turn 列总是填充空值。我没弄清楚我在哪里漏掉了它。

Answer 1

如果我没听错，你想为相同的 id_object 和 name 带来“结束回合”行的 start_datetime。在 MySQL 8.0 中，您可以为此使用 window 函数：

select t.*
from (
    select t.*,
        min(case when activity = 'End_turn' then start_datetime end)
            over(partition by id_object, name) as end_turn
    from mytable t
) t
where activity <> 'End_turn'

在早期版本中，替代方法是相关子查询：

select t.*,
    (
        select min(t1.start_datetime)
        from mytable t1
        where t1.id_object = t.id_object and t1.name = t.name and t1.activity = 'End_turn'
    ) as end_turn
from mytable t
where activity <> 'End_turn'

Answer 2

您的示例数据与您的查询不一致。

select  
  t1.id, <--- there is no column named as `id`. Instead it was `id_object`
  t1.name,
  t1.activity,
  DATE_FORMAT( t1.Start_DateTime, "%d/%m-%Y %H:%i:%s") as Start,
  (Select DATE_FORMAT(t1.Start_DateTime, "%d/%m-%Y %H:%i:%s")
    from Activities t2 
     WHERE t2.Activities = "End_turn" <---- there is no column named as `activities`. Instead it was `activity`.
   AND t2.id_object = t1.id_object) as end_activity
  FROM 
   Activities t1 
 WHERE 
 t1.Object_Prefix != ""
GROUP BY
t1.Start_DateTime

我已经使用您提供的示例数据尝试了您的查询，我得到了：

Error Code: 1242 Subquery returns more than 1 row

GROUP BY 在 t1.Start_DateTime 列上没有意义，因为它似乎在您的预期结果中清楚地表明您希望他们按 id_product 和 name.
您在 Start_DateTime 和 End_DateTime 列中的日期格式是 dd-mm-yyyy 而日期相关数据类型的标准 MySQL 日期是 yyyy-mm-dd.

最后，如果 Start_DateTime 和 End_DateTime 列的数据类型是 date/datetime，我建议这个查询：

SELECT id_object, `Name`, 
       SUBSTRING_INDEX(GROUP_CONCAT(Activity ORDER BY Start_DateTime ASC),',',1) ac, 
       MAX(CASE WHEN Object_Prefix <> '' THEN Object_Prefix END) op,
       MIN(CASE WHEN activity <> 'End_turn' THEN Start_DateTime END) sdt,
       MAX(CASE WHEN activity = 'End_turn' THEN Start_DateTime END) edt
FROM activities
GROUP BY id_object, `Name`;

你可以在这里看到演示：https://dbfiddle.uk/?rdbms=mysql_5.7&fiddle=de2af89c39e6636cfb45ee179cfb1461

SQL select inside select 使用日期时间列作为参考

SQL select inside select using a datetime column as reference

mysql

sql

datetime

subquery

where-clause