我有三张桌子
驱动程序
driver_id | driver_name |driver_number
----------------------------------------
1 | Driver 1 | 99999
2 | Driver 2 | 88888
每个司机都有班次
shift_id | start_time | end_time | driver_id
-----------------------------------------------------------------
4 |2015-04-02 10:09:00 |(NULL) | 1
3 |2015-04-02 09:19:00 |(NULL) | 2
2 |2015-04-02 11:09:00 |2015-04-02 19:09:00 | 1
1 |2015-04-02 10:09:00 |2015-04-02 20:09:00 | 2
在每次轮班期间,驾驶员可能会或可能不会多次出行
trip_id | start_time | end_time | shift_id
-----------------------------------------------------------------
12 |2015-04-02 10:09:00 |(NULL) | 4
11 |2015-04-02 09:19:00 |(NULL) | 4
10 |2015-04-02 11:09:00 |2015-04-02 19:09:00 | 3
9 |2015-04-02 10:09:00 |2015-04-02 20:09:00 | 2
8 |2015-04-02 10:09:00 |(NULL) | 4
7 |2015-04-02 09:19:00 |(NULL) | 4
6 |2015-04-02 11:09:00 |2015-04-02 19:09:00 | 3
5 |2015-04-02 10:09:00 |2015-04-02 20:09:00 | 4
4 |2015-04-02 10:09:00 |(NULL) | 4
3 |2015-04-02 09:19:00 |(NULL) | 4
2 |2015-04-02 11:09:00 |2015-04-02 19:09:00 | 2
1 |2015-04-02 10:09:00 |2015-04-02 20:09:00 | 1
我想得到一个查询,其中我获得最近的最多行程以及驾驶员详细信息,在开放班次(结束时间为null).
我一直在尝试的一切都失败了.
我理解查询应该是这样的:
select * from
drivers
inner join shifts on shifts.driver_id = drivers.driver_id
left join (some inner query on trips table) as trip
on shifts.shift_id = trip.trip_id
where shifts.end_time is null;
请帮我查询一下.预期的结果是这样的:
driver_id | driver_name | shift_id | shift_start_time | recent_trip_id | recent_trip_start_time
1 | Driver 1 | 4 | 2015-05-02 10:09:00 | 12 | 2015-04-02 10:09:00
2 | Driver 2 | 3 | 2015-05-02 11:09:00 | 10 | 2015-04-02 11:09:00
最佳答案 您可以使用变量来确定每个班次分区中的最近行程:
SELECT d.driver_id, d.driver_name, s.shift_id, s.start_time AS shift_start_time,
t.trip_id AS recent_trip_id, t.start_time AS recent_trip_start_time
FROM drivers AS d
INNER JOIN shifts AS s ON s.driver_id = d.driver_id
INNER JOIN (
SELECT trip_id, start_time,
@row_number:= CASE WHEN @sid = shift_id THEN @row_number+1
ELSE 1
END AS row_number,
@sid:=shift_id AS shift_id
FROM trips, (SELECT @sid:=0,@row_number:=0) as vars
ORDER BY shift_id, trip_id DESC ) t ON t.shift_id = s.shift_id AND t.row_number = 1
WHERE s.end_time IS NULL
谓词t.row_number = 1有效地选择每班最近的行程.查询的其余部分只是简单的JOIN子句,它们将驱动程序和(打开)移位数据聚集在一起.