the structure of the table is as follows: article table:
id title cid
1 xxx 5
2 xxx2 6
3 xxxx3 7
article_line relation table
article_id line_id
1 20
1 21
1 22
2 20
2 28
2 40
now the demand is: query line_id is equal to 20, and the article cid=6, and exclude the data of line_id=21, for example, the above article_id=2 is consistent, equal to 1 is not consistent
ask the Great God for help
select * from article where cid=6 and id in (select article_id from article_line where line_id=20)
query line_id equals 20, and the article cid=6, and excludes the requirement of line_id=21 ? Since Filter has only line_id=20, then the result set still needs to exclude line_id=21?.
is your real need to query all articles whose line_id is equal to 20 but not equal to 21?
this scenario uses the Exists statement
SELECT a.*
FROM article a
WHERE
EXISTS(SELECT al.article_id
FROM article_line al
WHERE al.line_id = 20 AND al.article_id = a.id)
AND NOT EXISTS(
SELECT al.article_id
FROM article_line al
WHERE al.line_id = 21 AND al.article_id = a.id)
)
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