两列引用另一个表中的一个ID

Question

I've been trying to work out the following but I can't get my head around it.

I need to match up the player IDs shown within the scores table to the persons table, and return the relevant person's name. Below is a condensed version of the tables showing the core parts of what's required.

Details will be returned based on the fixtures ID, so whatever person's ID falls on the same row I need to get their names.

Persons' ID is in the form of home_id_1, away_id_1, home_id_2, and away_id_2.

Persons Table
id fname lname
1 Fred Bloggs
2 John Brown
3 Kevin Smith
4 James Kirk

Scores Table
Fixtures_ID home_id_1 away_id_1 home_id_2 away_id_2
1 1 2 3 4

My current SELECT statement is:

SELECT scores.fixture_id, scores.match_date, players.fname, players.lname, 
       scores.home_id_1, scores.away_id_1, scores.home_id_2, scores.away_id_2  
    FROM scores, players  
    WHERE fixture_id = 1

Output should be something along the lines of:

Match Date Home Player 1 v Away Player 1, Home Player 2 v Away Player 2
10/01/2016 Fred Bloggs John Brown Kevin Smith James Kirk

Hope this makes sense, and any help is greatly appreciated.

Thanks,
Dan.

Answer 1

Try something like following

SELECT scores.fixture_id, 
       scores.match_date, 
       CONCAT(p1.fname, p1.lname), 
       CONCAT(p2.fname, p2.lname),
       CONCAT(p3.fname, p3.lname),
       CONCAT(p4.fname, p4.lname),    
       s.home_id_1, 
       s.away_id_1, 
       s.home_id_2, 
       s.away_id_2
FROM scores s 
    INNER JOIN players p1 ON s.home_id_1 = p1.id
    INNER JOIN players p2 ON s.away_id_1 = p2.id
    INNER JOIN players p3 ON s.home_id_2 = p3.id
    INNER JOIN players p4 ON s.away_id_2 = p4.id
WHERE s.fixture_id = 1

Maybe you need to use LEFT JOIN if you expect to have null values

Answer 2

You need to join to the players table four times, once for each column you want to match with it. Something like this:

SELECT 
  scores.fixture_id, 
  scores.match_date, 
  players1.fname + ' ' + players1.lname,
  players2.fname + ' ' + players2.lname,
  players3.fname + ' ' + players3.lname,
  players4.fname + ' ' + players4.lname,
FROM 
  scores, 
  INNER JOIN players players1 ON scores.home_id_1 = players1.id
  INNER JOIN players players2 ON scores.home_id_2 = players2.id
  INNER JOIN players players3 ON scores.away_id_1 = players3.id
  INNER JOIN players players4 ON scores.away_id_2 = players4.id
WHERE
  scores.fixture_id = 1