Calculating previous date in PostgreSQL

Question

I have a table of 'matches' :

id   match_date    home_team  away_team
---------------------------------------
 1   2012-10-01    Milan      Real
 2   2013-01-05    Real       PSG
 3   2013-04-05    Inter      Lacio
 4   2013-07-10    Ajax       Milan
---------------------------------------

1. How can I calculate previous match of each team? As example, for home team.
2. How can I calculate previous N-matches of each team?

Answer 1

Getting the previous matches is challenging, because of the home team/away team split. Instead, let's just focus on one team at a time, by having a separate record for each team.

The following gets the previous matchid for each team in the above table:

select id, match_date, team,
       lag(id) over (partition by team order by match_date) as prev_matchid
from ((select id, match_date, home_team as team, 'home' as which
       from matches
      ) union all
      (select id, match_date, away_team as team, 'away' as which
       from matches
      )
     ) m;

You can join in the information about the match, if you like.

Answer 2

You should be able to use the Max function to get the previous match. By selecting the max date that is less than today, you should be able to get the previous match.

Select Max(match_date), home_team, away_team 
from matches 
where match_date < current_date

To get the previous matches, you can order by match date

Select Match_date, home_team, away_team 
from matches 
order by match_date desc 
where match_date < current_date