Re: JOIN a table twice for different values in the same query - Mailing list pgsql-sql

Paul Lambert wrote:
> Colin Wetherbee wrote:
>> I would like to construct a query on the flight table that returns the 
>> names of both the departure port and the arrival port.
>>
>> The following query shows how I would get just the departure port.
>>
>> js=# SELECT departure_date, jsports.code AS departure_code FROM
>> jsjourneys JOIN jsports ON jsjourneys.departure_port = jsports.id LIMIT
>> 4;
>>
> Try joining twice, something like:
> 
> SELECT departure_date,
>        dp.code AS departure_code,
>        ap.code AS arrival_code
> FROM jsjourneys
> JOIN jsports dp ON jsjourneys.departure_port = jsports.id
> JOIN jsports ap ON jsjourneys.arrival_port=jsports.id
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend

Ah, I didn't realize you could alias tables inside the JOIN.  Excellent.  It works. :)

js=# SELECT departure_date, dp.code AS departure_code, ap.code AS 
arrival_code FROM jsjourneys JOIN jsports dp ON 
jsjourneys.departure_port = dp.id JOIN jsports ap ON 
jsjourneys.arrival_port = ap.id LIMIT 4;
 departure_date | departure_code | arrival_code
----------------+----------------+-------------- 2006-11-19     | BHM            | ATL 2006-11-16     | PIT
|ATL 2006-11-16     | ATL            | BHM 2006-10-26     | PIT            | BOS
 
(4 rows)

For archive completeness, note the query is joined relative to dp.id and 
ap.id, rather than jsports.id.

Thanks for your help!

Colin