Question

In Mysql, I want to select the bottom 2 items from each category

Category Value
1        1.3
1        4.8
1        3.7
1        1.6
2        9.5
2        9.9
2        9.2
2        10.3
3        4
3        8
3        16

Giving me:

Category Value
1        1.3
1        1.6
2        9.5
2        9.2
3        4
3        8

Before I migrated from sqlite3 I had to first select a lowest from each category, then excluding anything that joined to that, I had to again select the lowest from each category. Then anything equal to that new lowest or less in a category won. This would also pick more than 2 in case of a tie, which was annoying… It also had a really long runtime.

My ultimate goal is to count the number of times an individual is in one of the lowest 2 of a category (there is also a name field) and this is the one part I don’t know how to do.
Thanks

Answer 1

You could try this:

SELECT * FROM (
  SELECT c.*,
        (SELECT COUNT(*)
         FROM user_category c2
         WHERE c2.category = c.category
         AND c2.value < c.value) cnt
  FROM user_category c ) uc
WHERE cnt < 2

It should give you the desired results, but check if performance is ok.