将聚集查询与条件 SUM 比如：

SELECT
    p.username,
    SUM(CASE WHEN m.match_winner = m.team_a THEN m.team_a_odds ELSE m.team_b_odds END)
FROM 
    predictions p
    INNER JOIN matches m
        ON p.match_id = m.id AND p.team_id = m.match_winner
WHERE p.tournament_id = 30
GROUP BY p.username

SELECT
  USERNAME,
  SUM(IF(CASE WHEN MATCH_WINNER = TEAM_A, TEAM_A_ODDS, TEAM_B_ODDS))
FROM
  PREDICTIONS
INNER JOIN MATCHES
  ON MATCH_ID = MATCHES.ID AND 
    TEAM_ID = MATCH_WINNER
GROUP BY USERNAME;

但是自从 Neville predicted correctly match 7 and 9 (odds 2.4 + 2.0), total 4.4 points 不满足。。。

SELECT
  USERNAME,
  SUM( TEAM_B_ODDS)
FROM
  PREDICTIONS
INNER JOIN MATCHES
  ON MATCH_ID = MATCHES.ID AND 
    TEAM_ID = MATCH_WINNER
GROUP BY USERNAME;

op总是求团队的赔率
虽然我相信你 Naville 案例错误。