CODEWITHSUNDEEP
tagsrelationsql
Tomer W
Tomer W

Reputation: 3443

Selecting a row if it has all related options in a related table

Given a table definition:

Articles:
 art_id | name  
 -------|--------------
  1     | article1
  2     | article2
  3     | article3

Tags:
  tag_id | description
  -------|--------------
   1     | Scientific
   2     | Long
   3     | Short

article_tags:
  art_id | tag_id
  -------|---------
   1     | 1
   1     | 2
   2     | 1
   2     | 3
   3     | 1
   3     | 2
   3     | 3

The question is How to select all articles that are BOTH Scientific and Short?

Please note, it should be general for [2.N) tag combinations...

Upvotes: 4

Views: 2566

Answers (2)

jksloan
jksloan

Reputation: 184

SELECT    * 
FROM      articles 
WHERE     art_id IN 
          (
               SELECT    art_id 
               FROM      article_tags 
               GROUP BY  art_id 
               HAVING    COUNT(art_id) > 1
          )

Upvotes: 1

Taryn
Taryn

Reputation: 247860

You can use the following query to get the result:

select a.art_id, a.name
from articles a
inner join article_tags at
  on a.art_id = at.art_id
inner join tags t
  on at.tag_id = t.tag_id
where t.description in ('Short', 'Scientific')  -- tags here
group by a.art_id, a.name
having count(distinct t.tag_id) = 2 -- total count of tags here

See SQL Fiddle with Demo

Or this could be written:

select a.art_id, a.name
from articles a
inner join article_tags at
  on a.art_id = at.art_id
inner join tags t
  on at.tag_id = t.tag_id
group by a.art_id, a.name
having 
  sum(case when t.description = 'Short' then 1 else 0 end) >= 1 and
  sum(case when t.description = 'Scientific' then 1 else 0 end) >= ;

See SQL Fiddle with Demo.

If you just want to return the article id, then you could just query the article_tag table:

select art_id
from article_tags
where tag_id in (1, 3)
group by art_id
having count(distinct tag_id) = 2

See SQL Fiddle with Demo

Upvotes: 3

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