如何在一个sqlite命令中将多个行项目作为不同的列

Question

我有一张桌子看起来像这样：

Timestamp  direction  John  Mary  car   airplan

 4960        1        1   null   1     null
 5960        2        1     1   null    1  
 6960        1      null  null   1      1
 7960        1        1   null  null    1
 8960        2        1   null  null   null

记录的意思是：john / mary / together在时间戳记乘汽车/飞机返回xxx，我希望有一个单独的sqlite查询来获得如下结果：

          John_t          Mary_t       car_t      airplan_t
          0                0           6960        7960
          8960            5960            0          0

这表示（约翰，玛丽，汽车，飞机计划） （往/返）到xxx的最新时间戳。

我尝试sql命令，但是失败了...

select
(case when John=1 then max(Timestamp) else 0 end) as John_t, 
(case when Mary=1 then max(Timestamp) else 0 end) as Mary_t,
(case when car=1 then max(Timestamp) else 0 end) as car_t,
(case when airplan=1 then max(Time) else 0 end) as airplan_t
 from table where 4960 < Time < 8960 and group by direction

有人可以帮忙吗？

Answer 1

根据Andriy M的评论 ，这是答案：

select John_t, Mary_t, car_t, airplan_t from
    -- John --
    (select direction, (case when Timestamp=max_Timestamp then Timestamp else 0 end) as John_t from
        (
        (select dir.direction as direction, max(Timestamp) as Timestamp from
            (select distinct direction from trips) as dir
            left outer join
            (select * from trips where John = 1) as t
            on dir.direction = t.direction
            group by direction
        )
        cross join
        (select max(Timestamp) as max_Timestamp from trips where John = 1)
        )
    )
    natural join
    -- Mary --
    (select direction, (case when Timestamp=max_Timestamp then Timestamp else 0 end) as Mary_t from
        (
        (select dir.direction as direction, max(Timestamp) as Timestamp from
            (select distinct direction from trips) as dir
            left outer join
            (select * from trips where Mary = 1) as t
            on dir.direction = t.direction
            group by direction
        )
        cross join
        (select max(Timestamp) as max_Timestamp from trips where Mary = 1)
        )
    )
    natural join
    -- car --
    (select direction, (case when Timestamp=max_Timestamp then Timestamp else 0 end) as car_t from
        (
        (select dir.direction as direction, max(Timestamp) as Timestamp from
            (select distinct direction from trips) as dir
            left outer join
            (select * from trips where car = 1) as t
            on dir.direction = t.direction
            group by direction
        )
        cross join
        (select max(Timestamp) as max_Timestamp from trips where car = 1)
        )
    )
    natural join
    -- airplan --
    (select direction, (case when Timestamp=max_Timestamp then Timestamp else 0 end) as airplan_t from
        (
        (select dir.direction as direction, max(Timestamp) as Timestamp from
            (select distinct direction from trips) as dir
            left outer join
            (select * from trips where airplan = 1) as t
            on dir.direction = t.direction
            group by direction
        )
        cross join
        (select max(Timestamp) as max_Timestamp from trips where airplan = 1)
        )
    )
;

简要说明（从内部选择到外部）：

1. 我们将John / Mary / car / airplan的所有“行程” left outer join所有可能的方向进行left outer join联接。 这样可以确保每个约翰，玛丽，汽车和飞机计划的每个方向都有一行。 即使在该方向上没有“行程”，也需要稍后填写0 。
2. 我们将其“减少”为每个方向（ group by direction max(Timestamp)的最大时间戳（ max(Timestamp) ），因为我们对同一方向上的较早行程不感兴趣。

3. 将结果与John / Mary / car / airplan的整体最大时间戳交叉连接，以允许将较低的时间戳替换为0使用

    (case when Timestamp=max_Timestamp then Timestamp else 0) 

4. 我们为约翰，玛丽，汽车和飞机计划的每一个人做到这一点，并最终natural join一切融合在一起。