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sqlmysqlruby-on-railstagstagging

Sql query to find things with most specified tags

Let's say I have the following tables:

TAGS

id: integer
name: string

POSTS

id: integer
body: text

TAGGINGS

id: integer
tag_id: integer
post_id: integer

How would I go about writing a query that selects all posts in order of the post containing the highest number of the following tags (name attribute of tags table): "Cheese", "Wine", "Paris", "Frace", "City", "Scenic", "Art"

See also: Sql query to find things tagged with all specified tags (note: similar, but not a duplicate!)

Solution

  • Unlike your linked question, you did not specify here that you needed to match ALL tags. This query works for ANY.

    SELECT p.id, p.text, count(tg.id) as TagCount
    FROM Posts p 
        INNER JOIN Taggings tg 
            ON p.id = tg.post_id
        INNER JOIN Tags t 
            ON tg.tag_id = t.id
    WHERE t.name in ('Cheese', 'Wine', 'Paris', 'Frace', 'City', 'Scenic', 'Art')
    GROUP BY p.id, p.text
    ORDER BY TagCount DESC