php - PHP/MySQL 外键和显示表

Question

我有 3 个相互引用的表格。联赛、球队和球员。

联赛有leagueid,leaguename,city
球队有teamid,teamname,numberofplayers,leagueid(fk)
玩家有playid,playername,position,teamid(fk)

如何显示诸如 Players 之类的表格以显示所有内容并使用 teamid 外键显示他们的团队名称而不是该列？

Answer 1

SELECT Players.*, teamname
FROM Players JOIN Teams USING (teamid)

您只需要加入teamid两个表之间匹配的列。

Answer 2

您需要加入两个表使用INNER JOIN.

SELECT a.*, b.*
FROM   Players a
       INNER JOIN Teams b 
          ON a.teamid = b.teamid

要进一步了解有关联接的更多信息，请访问以下链接：

• SQL 连接的可视化表示

Answer 3

通过使用内连接

    SELECT  b.teamname,a.playername, a.position
       FROM   Players a
         INNER JOIN Teams b 
            ON a.teamid = b.teamid

如果您指定联赛，

  SELECT c.leaguename, c.city ,d.* FROM
    (SELECT  b.teamname,a.playername, a.position
       FROM   Players a
         INNER JOIN Teams b 
            ON a.teamid = b.teamid) d
            INNER JOIN Leagues c
                ON d.leagueid= c.leagueid