Question

I am currently working on a project to I fetch some information from an API and store it in a database. The table structure looks something like this:

id      ident aircraft_type  origin  destination  timestamp        departure_time
1      AWE1843      A321      KATL     KCLT    2012-10-04 10:46:34  2012-10-04 10:01:00 
2      ASQ5758      CRJ2      KATL     KIAD    2012-10-04 10:51:11  2012-10-04 09:40:00     
3      AAL2404      B738      KLAX     KDFW    2012-10-04 10:46:13  2012-10-04 08:23:00     
4      AAL2400      B738      KLAX     KDFW    2012-10-04 09:54:13  2012-10-04 07:31:00     
5      UAL912       B752      KLAX     KJFK    2012-10-04 10:19:24  2012-10-04 05:39:00
6      DAL1162      B752      KLAX     KCLT    2012-10-04 09:38:00  2012-10-04 04:44:30 

The six rows are for demonstration purposes; I have around 500 rows of such data. The application I am working on will ask the user to provide the two origin points and will provide the user with all the common destinations between those two origins.

For example, if a user enters “KATL” and “KLAX” as origin airports, the query displays the common destination between the two origins which is “KCLT”.

I tried different approaches to fix the issue but cannot get the desired functionality achieved. I tried joins and different ActiveRecord methods to no use.

Answer 1

Something like this will work it will give you both tables though, you can use s.* or e.* to pick specific table if you need to:

select * from (select * from flights where origin = 'KATL') s
inner join (select * from flights where origin = 'KLAX') e
on e.destination = s.destination;

If you just want to display destinations:

select distinct s.destination from (select * from flights where origin = 'KATL') s
inner join (select * from flights where origin = 'KLAX') e
on e.destination = s.destination;