How can I implement a boolean tag search in SQL?

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

I think this is what you're looking for:

SELECT * FROM TABLE_NAME WHERE COLUMN1 IN ('value1','value2','value3') AND COLUMN1 NOT IN ('value4','value5','value6')

If not, let me know. I may have misunderstood your question.

Answer 2

It depends on how you're storing tags in the database, but you probably want the IN operator:

SELECT tag FROM myTags WHERE tag IN ('p1','p2',...)
SELECT tag FROM myTags WHERE tag NOT IN ('p1','p2',...)

Answer 3

SELECT DISTINCT itemID FROM ItemsTags it, Tags t 
WHERE it.tagID = t.ID AND t.tag IN ('p1','p2','p3') AND t.tag NOT IN ('p4','p5','p6')

Answer 4

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

Answer 5

SELECT i.title
  FROM items i
 WHERE EXISTS(SELECT * FROM join_table j JOIN tags t ON t.id = j.tag_id WHERE j.item_id = i.id AND t.name = 'tag1')
   AND NOT EXISTS(SELECT * FROM join_table j JOIN tags t ON t.id = j.tag_id WHERE j.item_id = i.id AND t.name = 'tag2')

SQL server does a good job about this construct, but Oracle might need some hinting to get it right (at least it did 5 years ago).