自加入加入 table

Question

我的查询看起来像

Select m.cw_sport_match_id as MatchId,
       m.season_id as SeasonId,
       s.title as SeasonName,
       c.title as ContestName
from dbo.cw_sport_match m
inner join dbo.cw_sport_season s
  ON m.season_id = s.cw_sport_season_id
inner join dbo.cw_sport_contest c
  ON m.contest_id = c.cw_sport_contest_id
Where s.date_start <= GETDATE() AND s.date_end >= GETDATE()
order by s.date_start

不，我需要 sport_contest 的名称 parent（如果有的话，它可以为空）。所以基本上是一个自连接，但不在与查询相同的 table 上。我找到的所有自连接示例都没有在另一个 table 上完成。 sql 专业人士可以帮助我吗？那么我怎样才能将 cw_sport_season 本身与 season_parent_id 结合起来并获得它的标题呢？

Answer 1

如果我没有正确理解您的问题，您希望使用 season_parent_id 字段 outer join cw_sport_season table 自身。也许在这些方面：

Select m.cw_sport_match_id as MatchId,
       m.season_id as SeasonId,
       s.title as SeasonName,
       parent.title as ParentSeasonName,
       c.title as ContestName
from dbo.cw_sport_match m
inner join dbo.cw_sport_season s
  ON m.season_id = s.cw_sport_season_id
inner join dbo.cw_sport_contest c
  ON m.contest_id = c.cw_sport_contest_id
left join dbo.cw_sport_season parent
  ON s.season_parent_id = parent.cw_sport_season_id
Where s.date_start <= GETDATE() AND s.date_end >= GETDATE()
order by s.date_start

自加入加入 table

Self join on joined table

sql

sql-server

join

self-join