Question

Given a table of items, a table of tags and a join table between them, what is a good and efficient way to implement queries of the form:

p1 AND p2 AND ... AND pn AND NOT n1 AND NOT n2 ... AND NOT nk

I am using SQL. So to find all items that match all tags p1…pn and none of n1…nk?

Is there a good ‘standard’ solution for this?

Answer 1

Difficult to say without knowing your schema, but something like this would work:

select article_id from articles inner join tag t1 on t1.article_id=articles.article_id and t1.tag='included_tag' inner join tag t2 on t2.article_id=articles.article_id and t2.tag='another_included_tag' left outer join tag t3 on t3.article_id=articles.article_id and t3.tag='dont_include_tag' left outer join tag t4 on t4.article_id=articles.article_id and t4.tag='also_dont_include_tag' where t3.tag_id is null and t4.tag_id is null 

inner join to tags that are to be included, and do an anti-join (outer join + where a required column is null) to tags that are not to be included