如何 select 记录在另一个表中没有链接记录是 null？

Question

我有以下 SQL：

SELECT tournaments_blg.tournament_id_blg
FROM matches_blg  LEFT JOIN tournaments_blg ON tournaments_blg.tournament_id_blg = matches_blg.tournament_id_blg
WHERE matches_blg.match_id_op IS NULL
GROUP BY tournaments_blg.tournament_id_blg

这将选择所有tournaments_blg.tournament_id_blg _blg.tournament_id_blg，其中任何一个matches_blg.match_id_op是NULL 。

如果所有matches_blg.match_id_op都是NULL tournaments_blg.tournament_id_blg

Answer 1

SELECT tb.tournament_id_blg
FROM tournaments_blg tb
LEFT JOIN matches_blg mb ON tb.tournament_id_blg = mb.tournament_id_blg 
                        AND mb.match_id_op IS NOT NULL
WHERE mb.tournament_id_blg IS NULL

或者

SELECT tb.tournament_id_blg
FROM tournaments_blg tb
WHERE NOT EXISTS ( SELECT NULL
                   FROM matches_blg mb 
                   WHERE tb.tournament_id_blg = mb.tournament_id_blg 
                     AND mb.match_id_op IS NOT NULL )

Answer 2

尝试这个：

SELECT tournaments_blg.tournament_id_blg FROM matches_blg WHERE matches_blg.match_id_op NOT IN (Select tournaments_blg from tournaments_blg )