Which Key value pair database to be used

My Table has 2 columsn .Column1 is id,Column2 contains information  given by user about item in Column1 .User can give 3 types of information about item.I separate the opinion of single user by comma,and opinion of another user by ;.
I need to calculate opinions of all users very fast.My idea is to have index on key so the searching would be very fast.Currently i m using mysql .My problem is that maximum column size is below my requirement .If any overflow occurs i make new row with same id and insert data into new row.
Practically I would have around maximum 5-10 for each row.
I think if there is any database which removes this application code.
I just learn about key value pair database which is exactly i needed .
But which doesn't put constraint(i mean much better than RDMS on column size.
This application is not in production.