如何 select 记录在另一个表中没有链接记录是 null？

Question

I have the following 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

This selects all tournaments_blg.tournament_id_blg where any one of matches_blg.match_id_op is NULL .

How would I only select all tournaments_blg.tournament_id_blg if ALL the matches_blg.match_id_op are NULL ?

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

or

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

Try this:

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