Question

How would I combine (stack vertically) the following 3 queries into one query that returns 100 rows, 50 rows from category 1, 25 from from category 2, 25 from category 3 all chosen randomly. I tried UNION but didn’t seem to work.

select * from table where category_id = 1 order by rand() limit 50;

select * from table where category_id = 2 order by rand() limit 25;

select * from table where category_id = 3 order by rand() limit 25;

Answer 1

To apply ORDER BY or LIMIT to an individual SELECT, place the clause inside the parentheses that enclose the SELECT:

(select * from table where category_id = 1 order by rand() limit 50)
UNION ALL
(select * from table where category_id = 2 order by rand() limit 25)
UNION ALL
(select * from table where category_id = 3 order by rand() limit 25);