MySQL的加入問題

Question

我有以下表：

--table sportactivity-- 

sport_activity_id, home_team_fk, away_team_fk, competition_id_fk, date, time 

（例如元組） - > 1，33，41，如圖5所示，2010-04-14，5時40分○○秒

--table teams-- 

team_id, team_name 

（元組的例子） - > 1，阿爾及利亞

現在我有用於提取球隊A對B隊

SELECT sport_activity_id, T1.team_name AS TeamA, T2.team_name AS TeamB, DATE_FORMAT(DATE, '%d/%m/%Y') AS DATE, DATE_FORMAT(TIME, '%H:%i') AS TIME 

FROM sportactivity 

JOIN teams T1 ON home_team_fk = T1.team_id 

JOIN teams T2 ON (away_team_fk = T2.team_id 

OR away_team_fk = '0') 

WHERE DATE(DATE) >= CURDATE() 

ORDER BY DATE(DATE) 

以下SQL statment 210

我的問題是，當B隊是空的，我有無關的信息....它似乎是它返回所有的組合。我需要一個查詢，當B隊等於0時（這可以發生在我的場景中）我只得到隊A - 隊B（作爲0）一次。

Answer 1

使用LEFT OUTER JOIN而不是INNER JOIN。也就是說，改變此：

JOIN teams T2 ON (away_team_fk = T2.team_id OR away_team_fk = '0') 

這樣：

LEFT JOIN teams T2 ON away_team_fk = T2.team_id 

這應該在away_team_fk = 0（假定沒有這樣的行存在）的情況下在T2返回空值的列。

Answer 2

您是否嘗試過使用DISTINCT關鍵字？

SELECT DISTINCT sport_activity_id, T1.team_name AS TeamA, T2.team_name AS TeamB, DATE_FORMAT(DATE, '%d/%m/%Y') AS DATE, DATE_FORMAT(TIME, '%H:%i') AS TIME 

FROM sportactivity 

JOIN teams T1 ON home_team_fk = T1.team_id 

JOIN teams T2 ON (away_team_fk = T2.team_id 

OR away_team_fk = '0') 

WHERE DATE(DATE) >= CURDATE() 

ORDER BY DATE(DATE) 

這將確保如果一行重複，所有數據相同，它只顯示一次。

一樣，如果你有

1 abc abc 10/22/10 12:00:00 
1 abc abc 10/22/10 12:00:00 
2 abc dcb 10/22/10 12:00:00 

你將不得不

1 abc abc 10/22/10 12:00:00 
2 abc dcb 10/22/10 12:00:00 

返回，而不是