如何按特定顺序选择(几乎)唯一值

Question

在一次旅行中,有几个站点(一个站点=一个地址,其中一个或多个订单被加载或交付),按特定顺序.例如:

Trip A
Trip_order   Action   Place          Ordernumber
10           Load     Paris          394798
20           Load     Milan          657748
30           UnLoad   Athens         657748
40           Unload   Thessaloniki   394798
50           Load     Thessaloniki   10142
60           Load     Thessaloniki   6577
70           Unload   Athens         6577
80           Unload   Athens         10412
90           Load     Thessaloniki   975147
100          Unload   Paris          975147

我希望按行程顺序查看具体的停靠点:

Load Paris
Load Milan
Unload Athens
Unload Thessaloniki
Load Thessaloniki
Unload Athens
Load Thessaloniki
Unload Paris

我确实看过这个,但如果我这样做,我只能卸载雅典,卸载塞萨洛尼基并加载塞萨洛尼基一次.

我该如何解决这个问题？

编辑:11:11(UTC +01:00)更具体一点:这些是提供此信息的表格:

Trips
Trip_ID
100001  
100002
100003
....

Actions
Trip_ID  Action MatNr RoOr RoVlg    OrderID
100001   1      10      10     1     394798
100001   1      10      20     1     657748
100001   1      10      30     1     657748
100001   1      10      40     1     394798
100001   1      10      50     1      10142
100001   1      10      60     1       6577
100001   1      10      70     1       6577
100001   1      10      80     1      10412
100001   1      10      90     1     975147
100001   1      10     100     1     975147

(动作:1 =加载,4 =卸载)MatNr,RoOr和RoVlg的组合是Trip的顺序.

Orders
OrderID LoadingPlace UnloadingPlace
6577    Thessaloniki Athens
10142   Thessaloniki Athens
394798  Paris        Thessaloniki
657748  Milan        Athens
975147  Thessaloniki Paris

Answer 1

试试这个吧.没有变数,没什么特别的花哨:

select a1.action, a1.place
  from trip_a a1
    left join trip_a a2
      on a2.trip_order = 
        (select min(trip_order) 
          from trip_a a3 
          where trip_order > a1.trip_order)
  where a1.action != a2.action or a1.place != a2.place or a2.place is null

在这里演示:http://sqlfiddle.com/#!9/4b6dc/13

希望它适用于你正在使用的任何sql,它应该,只要支持子查询.

Tt只是找到下一个最高点trip_id,并加入它,或者null如果没有更高的值则加入trip_order.然后,它仅选择行,其中任一place中,action或这两者是不同的,或者如果没有发生在连接表(a2.place is null).

标准完全改变后编辑

如果要获得完全由基表构建的相同结果,可以执行以下操作:

  select 
         case when a.action = 1 then 'load' when a.action = 0 then 'unload' end as action,
         case when a.action = 1 then o.loadingplace when a.action = 0 then o.unloadingplace end as place
    from trips t
      inner join actions a
        on t.trip_id = a.trip_id
      inner join orders o
        on a.orderid = o.orderid
      left join actions a2
        on a2.roor = 
          (select min(roor) 
             from actions a3
             where a3.roor > a.roor)
      left join orders o2
        on a2.orderid = o2.orderid
      where a.action != a2.action
        or a2.action is null
        or
          case when a.action = 1 then o.loadingplace != o2.loadingplace
               when a.action = 0 then o.unloadingplace != o2.unloadingplace
          end
    order by a.roor asc

这里有一个更新的小提琴:http://sqlfiddle.com/#!9/ fdf9c/14