Question

我的表格看起来像这样：

FlightLeg

+------+-----+-------+------+---------------------+---------------------+-------+
| FLNO | Seq | FromA | ToA  | DeptTime            | ArrTime             | Plane |
+------+-----+-------+------+---------------------+---------------------+-------+
| 1000 |   1 | DFW   | LOG  | 2020-01-01 01:10:20 | 2020-01-01 01:13:40 |     7 |
| 1010 |   1 | LAX   | ORD  | 2020-01-01 01:13:10 | 2020-01-01 01:16:20 |     3 |
| 1020 |   1 | LOG   | JFK  | 2020-01-01 01:05:40 | 2020-01-01 01:06:20 |     9 |
| 1030 |   1 | LAX   | INT  | 2020-01-01 01:11:20 | 2020-01-01 01:16:10 |     6 |
| 1040 |   1 | LAX   | LGA  | 2020-02-01 01:15:30 | 2020-01-01 01:21:00 |     1 |
| 1010 |   2 | ORD   | JFK  | 2020-01-01 01:17:10 | 2020-01-01 01:20:20 |     3 |
| 1020 |   2 | JFK   | DFW  | 2020-01-01 01:07:20 | 2020-01-01 01:10:20 |     9 |
| 1030 |   2 | INT   | DFW  | 2020-01-01 01:17:20 | 2020-01-01 01:18:00 |     6 |
| 1020 |   3 | DFW   | INT  | 2020-01-01 01:11:10 | 2020-01-01 01:11:40 |     7 |
| 1020 |   4 | INT   | LAX  | 2020-01-01 01:12:20 | 2020-01-01 01:15:10 |     7 |
+------+-----+-------+------+---------------------+---------------------+-------+

而且：

飞行

+------+--------+---------+
| FLNO | Meal   | Smoking |
+------+--------+---------+
| 1000 | Bistro | Y       |
| 1010 | Meal   | N       |
| 1020 | Meal   | Y       |
| 1030 | Snack  | N       |
| 1040 | Meal   | N       |
+------+--------+---------+

我试图写一个查询，其中每个航班有两条腿以上，检索航班号（FLNO），第一个出发城市（FromA）和最后到达的城市。飞行序列可以从一个任意整数开始，并可以用任意整数偏移量分开。

这是我到目前为止所做的：

SELECT FlightLeg.FLNO, (
SELECT FlightLeg.FromA
FROM FlightLeg
INNER JOIN Flight
ON FlightLeg.FLNO=Flight.FLNO
GROUP BY FlightLeg.FLNO
HAVING COUNT(*) > 2),
(
SELECT FlightLeg.ToA
FROM FlightLeg
INNER JOIN Flight
ON FlightLeg.FLNO=Flight.FLNO
GROUP BY FlightLeg.FLNO
HAVING COUNT(*) > 2)

FROM FlightLeg
INNER JOIN Flight
ON FlightLeg.FLNO=Flight.FLNO
GROUP BY FlightLeg.FLNO
HAVING COUNT(*) > 2;

所有我能得到的输出是FLNO，FromA，正确航班的第一序列的ToA。

预期产出：

+------+-------+------+
| FLNO | FromA | ToA  |
+------+-------+------+
| 1020 | LOG   | LAX  |
+------+-------+------+

我认为我非常接近，但我不确定如何找到FromA，最小序列和最大序列的ToA。

有人可以帮忙吗？谢谢！

Answer 1

解决此问题的一种方法是使用自连接和派生表，如下所示：

select flight_start.flno, flight_start.froma, flight_end.toa 
from flightleg flight_start
join flightleg flight_end on flight_start.flno = flight_end.flno
join (
  select 
    flno,
    min(seq) origin,
    max(seq) destination
  from flightleg
  group by flno
  having count(*) > 2
) min_max_seq
 on flight_start.flno = min_max_seq.flno 
and flight_start.seq  = min_max_seq.origin
and flight_end.seq    = min_max_seq.destination

用作派生表的查询确定每个航班的最低和最高序号，第一个联接使用较低序列号来检索原始机场，而第二个联接使用较高序列号来检索目的地机场。腿数由派生表中的having子句确定。

在旁注中：如果序列号不是订单的一个好的决定因素，那么您可以使用日期来确定订单或订单。

Sample SQL Fiddle

Answer 2

select  x.flno, 
        Max( if( y.DeptTime = x.starter, y.FromA, null )) FirstLegFrom,
        Max( if( y.DeptTime = x.starter, y.DeptTime, null )) FirstLegStart,
        Max( if( y.DeptTime = x.ender, y.ToA, null )) LastLegFrom,
        Max( if( y.DeptTime = x.ender, y.ArrTime, null )) LastLegArrival
from(
    select  flno, min(depttime) as starter, max(depttime) as ender
    from    flightleg
    group by flno
    having count(*) > 2
) x
join   flightleg y
  on   x.flno = y.flno
  and  (x.starter = y.depttime
    or  x.ender = y.depttime)
group by x.flno;

小提琴：http://sqlfiddle.com/#!9/79640/1/0 （由TommCatt提议进行修改以提高效率）

这不依赖于seq每个航班的升序。

从SQL表中获取值

2 个答案: