Getting only 4 rows per idea from ideas table
As the comments mentioned, your question is lacking a lot of details. Specifically what is the criteria / logic you want to use to select 4 rows when idea with id = DC889 has 10 rows, for example?
In any case, this will get you a random set of 4 rows for idea DC889:
SELECT * -- Replace * with only the columns you need, as * is bad practice
FROM IdeaTable
WHERE id = 'DC889'
LIMIT 4;