Question

I have a many to many relationship between entries and keywords with a join table entries_keywords. I want to fetch all entries for both the keys ‘wake’ and ‘up’. The only way I came up with is this. If I want to throw in another search word it gets even worse. How do you refactor this? Is there another way to join it than using subqueries?

select * 
from 
(
    select * 
    from entries e 
    inner join entries_keywords ek 
        on e.id = ek.entry_id 
    inner join keywords k 
        on ek.keyword_id = k.id 
    where k.key = 'wake'
) e 
inner join entries_keywords ek 
    on e.id = ek.entry_id 
inner join keywords k 
    on ek.keyword_id = k.id 
where k.key = 'up';

Answer 1

If you only want to retrieve entries that have at least one of the keywords, you can do:

SELECT
    a.*
FROM
    entries a
INNER JOIN
    entries_keywords b ON a.id = b.entry_id
INNER JOIN
    keywords c ON b.keyword_id = c.id
WHERE
    c.key IN ('wake', 'up')

If you want to retrieve entries that have ALL of the keywords in the list, add GROUP BY and HAVING:

SELECT
    a.*
FROM
    entries a
INNER JOIN
    entries_keywords b ON a.id = b.entry_id
INNER JOIN
    keywords c ON b.keyword_id = c.id
WHERE
    c.key IN ('wake', 'up')
GROUP BY
    a.id
HAVING
    COUNT(*) = 2

Where 2 is the number of keywords in the list you’re checking on.