Advanced MySQL Joining. Speeding up query

Question

I have a list of users on my php application (using codeigniter). Each user may have completed a form with about 1000 or so total fields. The structure looks similar to this:

Answer 1

I'm not sure I completely understand the problem. You can use a single query to get all users, and all of their fields (basically, this is what Philip suggested):

SELECT u.username, f.* 
FROM user AS u
    INNER JOIN completed_form_fields AS f
    ON f.userid = u.id
ORDER BY u.id, f.fieldkey

To filter the results, add a WHERE clause with the conditions. For example, to only get data from fieldkeys 'k1', 'k2' and 'k3':

SELECT u.username, f.* 
FROM user AS u
    INNER JOIN completed_form_fields AS f
    ON f.userid = u.id
WHERE f.fieldkey IN ('k1', 'k2', 'k3')
ORDER BY u.id, f.fieldkey

Is this what you're looking for?