how can I get a DISTINCT from mySQL but only for 1 field?

Question

I have a row with products and I'd like to get 10 random records, but a maximum of 1 row per user_id. Right now I have this:

SELECT user_id, product_id, price, name, category, is_featured 
FROM db_products
WHERE category!=15 AND active=1 AND deleted=0 AND is_featured=1 
ORDER BY RAND() DESC LIMIT 0,12

I tried doing a SELECT DISTINCT user_id, ... but that doesn't work. The table has 100's of products and each user_id may have multiple ones, but I'd like to retrieve a maximum of 1 per user_id, but still a total of 10.

Is that possible at all without a more complex structure?

Answer 1

I may be missing something, but have you tried doing a GROUP BY?

SELECT user_id, product_id, price, name, category, is_featured 
FROM db_products
WHERE category!=15 AND active=1 AND deleted=0 AND is_featured=1 
GROUP BY user_id -- SPECIFY FIELD HERE
ORDER BY RAND() DESC 
LIMIT 0,12

This will group one row per user, or whichever field you desire to group by.

Answer 2

Try something like that with grouping in main query after random ordering in subquery:

SELECT * FROM
(SELECT user_id, product_id, price, name, category, is_featured 
FROM db_products
WHERE category!=15 AND active=1 AND deleted=0 AND is_featured=1 
ORDER BY RAND()) AS subquery
GROUP BY user_id
LIMIT 0,10