如何比较来自两个不同表SQL的数据

Question

This maybe simple but I'm not sure how to go about it. I have 2 tables Match and Players

Players table
-------------
PlayerID     int
PlayerName   varchar(20)
TeamID       int
TeamName     varchar(10)

Match table
-----------
MatchID         int 
Team1           varchar(20)
Team2           varchar(20)
MatchDate       date

For example for a specific match I would like to list all player names from both teams.

Say 28/03/16 Liverpool vs Arsenal , how do I get the player names from the Players table?

Anything you could tell me will help.

Answer 1

Instead of storing team names as team1 and team2 in your match table, store their corresponding team ids.

Edit : Every match should unique match id, so that date filter is not required.

This could help you to retrieve records using the query :

select * from players a where exists(select 1 from match b where 
b.MATCH_ID= :match_id and (a.team_id=b.team1 OR
a.team_id =b.team2))

Answer 2

Get the row from match table. If you don't know if team1 is Liverpool or Arsenal, or vice versa for team2

 SELECT m.matchid
   FROM match m
  WHERE m.date = TO_DATE('2016-03-28','YYYY-MM-DD')
    AND m.team1 IN ('Liverpool','Arsenal')
    AND m.team2 IN ('Liverpool','Arsenal')
    AND m.team1 <> m.team2

Next, make two copies of the row...

 SELECT m.matchid
   FROM (SELECT 1 AS i UNION ALL SELECT 2) d
  CROSS
   JOIN match m
  WHERE m.date = TO_DATE('2016-03-28','YYYY-MM-DD')
    AND m.team1 IN ('Liverpool','Arsenal')
    AND m.team2 IN ('Liverpool','Arsenal')
    AND m.team1 <> m.team2

The perform join to the players table, looks like we use teamname column to match.

 SELECT CASE WHEN d.i = 1 THEN m.team1 ELSE m.team2 END AS teamname
      , p.playername
   FROM (SELECT 1 AS i UNION ALL SELECT 2) d
   JOIN match m
     ON m.date = TO_DATE('2016-03-28','YYYY-MM-DD')
    AND m.team1 IN ('Liverpool','Arsenal')
    AND m.team2 IN ('Liverpool','Arsenal')
    AND m.team1 <> m.team2
   LEFT
   JOIN players p
     ON p.teamname IN (m.team1, m.team2) 
  ORDER BY d.i, p.playerid