MySQL返回一些行3次

Question

我有这个问题:

SELECT w.windate, w.wintime, w.field, w.htname, w.vtname, w.plateumpire, 
       w.fieldumpire1, w.fieldumpire2, w.fieldumpire3, p.pteamname, p.teamcoach, 
       p.pteamdivision, d.originalid 
    FROM sportsdb_wins AS w, playerteams AS p, sportsdb_divs AS d 
    WHERE p.teamcoach='$coachid' 
        AND p.pteamname IN (w.htname, w.vtname) 
        AND p.forteam='$teamid'

并且至少有一行返回3次!为什么？请帮忙我是SQL新手.在PHP中使用它...

Answer 1

必须加入表时使用JOIN.您当前的问题是所谓的笛卡尔积.