SQL帮助无法解决有关内部联接的此查询

Question

我必须弄清楚哪些游泳运动员在同一场比赛中获得了相同的位置。对于每对这样的游泳运动员，我必须显示一行，显示每个游泳运动员的比赛ID，地点和参赛者数量。示例

eventid  place  competitors tied

SWM012  2   1072528 1099641

SWM021  2   1018529 1061698

这是我目前的代码

select R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum
from Results R1, Results R2 
where R1.Place = R2.Place
group by R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum

这是输出

eventid  Place   competitornum    competitornum

SWM010   1       1121587           1056740

SWM010   1       1121587           1061698

以及第二列竞争对手栏中第一列不同的竞争对手

我只是想知道如何获得输出，如上面的描述

Answer 1

首先，您可能还需要加入事件ID

select R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum
from Results R1, Results R2 
where R1.Place = R2.Place AND R1.EventId = R2.EventId
group by R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum

上述查询返回与此

相同的结果

select distinct R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum
from Results R1, Results R2 
where R1.Place = R2.Place AND R1.EventId = R2.EventId

但这将返回所有独特的“关系”对。一个解决方案就是这个

select distinct R1.Eventid, R1.Place, R1.Competitornum, R2.Competitornum
from Results R1, Results R2 
where R1.Place = R2.Place AND R1.EventId = R2.EventId AND R1.Competitornum > R2.Competitornum

这只适用于双向联系。