mysql - How to use SQL to get records that are distributed evenly from each category? -

i have table this:

category_id    uid    popularity   ts =======================================     03     05     07     07     07     10     10 

for each row, uid unique , each row belongs category, presented category_id. let's have 10 categories in total , there thousands of records.

i try make sql query 50 records within timeframe sorted popularity. can done. however, if hope these 50 records distributed evenly each category? example, if there 10 categories, each has 5 records, there 50 records in total. there way via 1 sql query? or have in 10 separate sql queries?

select * mytable categoryid = 1 order popularity desc limit 10 union select * mytable categoryid = 2 order popularity desc limit 10 union select * mytable categoryid = 3 order popularity desc limit 10 

repeat many categories have

some mysql wizard can tell how group by too.

see: unions