Question

I need some help with this query: I want to delete the following rows from my table.
The table has 4 columns: UserID, UserName, Tag, Score.

I want to keep only the top 1000 users with highest score, for each Tag.

So I need to order by score, and to keep the first 1000 users for each tag.

Thanks

Answer 1

Based on the other answer,

DELETE FROM table t1
WHERE UserID NOT IN (SELECT userID FROM table t2
                     WHERE t2.tag = t1.tag
                     ORDER BY Score DESC LIMIT 1000);

This assumes that UserID is a unique/primary key field. If it’s not, you could do something like this:

DELETE FROM table t1
WHERE UserID||' '||Tag NOT IN (SELECT UserID||' '||Tag FROM table t2
                     WHERE t2.tag = t1.tag
                     ORDER BY Score DESC LIMIT 1000);

Putting the spaces in because I know I’ve had to do similar on Oracle, not sure how MySQL would handle it without.