Question

I am writing code (using MySQL) to solve a problem similar to the following:

There are 20 boolean options (per every user).

Should I store 20 ENUM('false','true') or put into a table only IDs of these options which are true (so probably having less than 20 rows per user)?

Answer 1

If new options are likely to appear and you don’t filter by the options, you may as well go with a EAV structure (a record per option).

This way, you can add new options more easily (no change to metadata).

Assuming that the options values are either TRUE or FALSE (no NULL possible), you should create records only for non-default option values (TRUE in your case). An absence of the record would mean false.

To retrieve all options, you could use this:

SELECT  *, GROUP_CONCAT(CONCAT(o.id, ': ', ov.user IS NULL), ', ' ORDER BY o.id)
FROM    users u
CROSS JOIN
        options o
LEFT JOIN
        option_value ov
ON      (ov.user, ov.option) = (u.id, o.id)
GROUP BY
        u.id

, which would give you dynamic output:

user_id   options
1         1: 0, 2: 1, 3: 0