JOIN 2 tables, and query data from them 3 times

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Question :

Basically I have 2 tables: post_meta and posts.

post_meta has a post_id, key and value:

post_id  key      value
6343     make     Chevy
6343     model    Volt
6794     make     Chevy
6794     model    Silverado

posts has a post_id and content:

post_id  content
5434     Hello World!
6343     Chevy Volt review
6794     The New Silverado

What I need to do is pull the model based on the make (pull all unique models with the make “Chevy”). The database isn’t very big so it doesn’t need to be a real fast query. Basically the plan in my mind was to get the model of every post_id that has the post_meta.make “Chevy”.

SELECT post_id FROM postmeta
WHERE key = 'make'
AND value = 'Chevy'

then take the post_id

SELECT DISTINCT value FROM postmeta
WHERE post_id = {an array of post_id's}

something to that extent.

Answer :

Given your table structure, this should extract what you are looking for:

SELECT DISTINCT p1.value
FROM postmeta p1
INNER JOIN postmeta p2 ON p1.post_id = p2.post_id
WHERE p2.key = 'make'
    AND p2.value = 'Chevy'
    AND p1.key = 'model';

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