[英]MySQL Join tables with a condition
我的SQL不是这个,但我很确定SQL大师很容易 - 我宁愿找出正确的查询,而不是把逻辑放到PHP脚本中......
所以:我有两张桌子,一张包含一个俱乐部的信息,一个特定的比赛以及俱乐部为这场比赛输入的球队数量。 第二个表将条目拆分为“分区”
即
mysql> describe Entries;
+----------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| ClubId | int(11) | NO | PRI | NULL | |
| MatchId | int(11) | NO | PRI | NULL | |
| NumTeams | int(11) | NO | | NULL | |
+----------+---------+------+-----+---------+-------+
mysql> describe Divisions;
+----------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| MatchId | int(11) | NO | MUL | NULL | |
| ClubId | int(11) | NO | MUL | NULL | |
| Team | int(11) | NO | | NULL | |
| Division | int(11) | NO | | NULL | |
+----------+---------+------+-----+---------+-------+
样本数据:
Entries:
1, 1, 1 (Club1, Match1, 1 team)
1, 3, 2 (Club1, Match3, 2 teams)
Divisions:
1, 1, 1, 1 (Club1, Match1, Team1 is in division 1)
1, 1, 2, 2 (Club1, Match1, Team2 is in division 2)
1, 2, 1, 1 (Club1, Match2, Team1 is in division 1)
1, 2, 2, 2 (Club1, Match2, Team2 is in division 2)
1, 3, 1, 1 (Club1, Match3, Team1 is in division 1)
1, 3, 2, 2 (Club1, Match3, Team2 is in division 2)
要求的结果:
1, 1, 1 (Club 1, Match1, Team1)
1, 3, 1 (Club1, Match3, Team1)
1, 3, 2 (Club1, Match3, Team2)
- so not all the rows in Divisions are in the result.
e.g, club1, match1, team2 isn't here because there
is only one entry in match 1.
现在,当俱乐部进入或移除球队时,Entries.NumTeams可以上下起伏。 当一个新团队进入时,它会被放入第1部分(就这样它总是在一个部门中)。 当团队被移除时,他们在分区表中的输入不会被删除(分区是手动设置的,所以如果有人决定俱乐部X的第二队属于分区2,即使俱乐部X还没有进入第二队,你也希望保留这些信息球队)。
所以,要打印一个部门的所有团队,我需要这样的东西:
SELECT * FROM Divisions WHERE Divisions.Team <= Entries.NumTeams
(for the Entries row with the matching match and club)
我试过这个:
SELECT Divisions.* from Entries LEFT JOIN Divisions ON
Divisions.MatchId = Entries.MatchId AND Divisions.ClubId = Entries.ClubId
WHERE Divisions.Team <= Entries.NumTeams
但我最终得到了重复的行。 我可以通过使用SELECT DISTINCT来摆脱它们,但这让我觉得我的查询已经被打破了。 我还交换了哪个表左右,但仍然有重复。
将在明天尝试提供的答案。 谢谢!
使用DISTINCT
将删除重复行,您的查询似乎没问题。
在mysql中使用distinct
SELECT distinct Divisions.* from Entries LEFT JOIN Divisions ON
Divisions.MatchId = Entries.MatchId AND Divisions.ClubId = Entries.ClubId
WHERE Divisions.Team <= Entries.NumTeams
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