好吧，您确实需要
SUM这些列（这
SUM是一个聚合函数，这就是为什么要在
GROUPBY那儿使用）。为了更好地编写查询，您需要丢失旧的隐式
JOIN样式，并使用ANSI显式样式：
SELECt game.mdate, game.team1, SUM(CASE WHEN goal.teamid=game.team1 THEN 1 ELSE 0 END) score1, game.team2, SUM(CASE WHEN goal.teamid=game.team2 THEN 1 ELSE 0 END) score2FROM gameINNER JOIN goal ON game.id=goal.matchidGROUP BY game.mdate, goal.matchid, game.team1, game.team2
