Question

SELECT teams.teamname AS Home, 
       teams.teamname AS Away 
FROM   game 
       LEFT JOIN teams 
              ON game.awayteam = teams.teamid 
       LEFT JOIN teams AS T 
              ON game.hometeam = T.teamid

我的表格如下

Game                                     
-GameId(Pk,int),
-HomeTeamId (fk,int),   
-AwayTeamId(fk,int)                     

Teams
-TeamId(Pk,int),
-TeamName(Varchar)

我正在尝试在查询中查看主队和客队名。当我加入表时，我的预期结果是主队名和客队名，但是在两个表中只列出了主队名。

Home Team|Spikes

Away Team|Spikes

什么时候应该

Home Team|Spikes

Away Team|Raptors

Answer 1

您需要让两个加入别名。您正在选择第一次加入的结果两次。

e.g。

SELECT
  GameId,
  home.TeamName AS Home,
  away.TeamName AS Away
FROM Game
  LEFT JOIN Teams AS away ON AwayTeamId = away.TeamId
  LEFT JOIN Teams AS home ON HomeTeamId = home.TeamId;

Answer 2

如果将重命名列重命名为联接中的表表达式，则可以使用NATURAL JOIN并完全避免使用范围变量。另外，我不相信你真的需要外连接：

SELECT Home, Away
  FROM game
       NATURAL JOIN
       ( SELECT teamid AS hometeam
              teamname AS home
         FROM teams ) Home
       NATURAL JOIN
       ( SELECT teamid AS awayteam
              teamname AS Away
         FROM teams ) away;

无法使用左连接将两个键连接到一个主键

2 个答案: