Re: error code 1241, operand should contain 1 column(s)

[Peter Brawley]

...Where horse_id in(select...) requires that (select...) returns a single value. Your (select...) returns two. You need something like this ...

Select horse_id, Name 
From horse 
Join (
  Select horse_id, count(*) as wins 
  From entry 
  where place <=3 
  having count(*) > 1
) x using(horse_id);