选择一组ID的先前记录

Question

我有这样的查询：

SELECT id, id_employee, hours FROM WorkHours WHERE hours > 8;

如何为此查询选择的每个人选择上一个员工工作记录？

所以，对于这样的表（id，id_employee，hours）：

1 - 1 - 5
2 - 2 - 3
3 - 1 - 9
4 - 1 - 4
5 - 2 - 4
6 - 2 - 10
7 - 2 - 7
8 - 1 - 7
9 - 2 - 9

将选择记录3,6和9。我还得到了什么记录1,5,7。基本上，每当有人加班时，我想看看这个人在之前录制的那一天有多少小时。

Answer 1

您可以使用相关子查询获取之前的id：

SELECT wh.id, wh.id_employee, wh.hours,
       (SELECT MAX(wh2.id)
        FROM WorkHours wh2
        WHERE wh2.id_employee = wh.id_employee AND wh2.id < wh.id
       ) as prev_id
FROM WorkHours wh
WHERE wh.hours > 8;

然后，要获得完整行，请使用JOIN：

SELECT eh.*, wh.*
FROM (SELECT wh.id, wh.id_employee, wh.hours,
             (SELECT MAX(wh2.id)
              FROM WorkHours wh2
              WHERE wh2.id_employee = wh.id_employee AND wh2.id < wh.id
             ) as prev_id
      FROM WorkHours wh
      WHERE wh.hours > 8
     ) eh LEFT JOIN
     WorkHours wh
     ON wh.id_employee = eh.id_employee;