mysql 分组后，在每个组中排序

如下数据：

活动id  批次id  批次开始时间  期望序号

1           1           09:00               1

1            2          09:01                2

1            3          09:05               3

2            4          08:55               1

2            5          09:00               2

.........

活动id ：choose_room_activity_id

批次id： choose_room_batch_id

开始时间： start_date

表名：ztc_choose_room_batch

select a.choose_room_activity_id,a.choose_room_batch_id,count(*) as 序号,a.start_date from ztc_choose_room_batch as a
INNER JOIN ztc_choose_room_batch as b
ON a.choose_room_activity_id=b.choose_room_activity_id and a.start_date >= b.start_date group by a.choose_room_activity_id,a.choose_room_batch_id ORDER BY a.start_date asc;