Adding data to the end of a mySQL field [PHP]

Hi there, and thank you for you time.

I’m currently learning OOP with php. I have a ‘user’ mySQL table with ‘id’, ‘username’, and ‘savedItems’ as well as a ‘items’ mySQL table with ‘id’, ‘title’, etc…

I want to be able to add numerous item ids to the ‘savedItems’ field in my user table so that later i can seperate them using split().

Say i have 2 ids already in that field (25,48) how can i add another one to the end (25,48,31)?
I understand i would use ‘UPDATE’ but all I know how to do is update the entire field.

Should i echo the field origionally and add the new info to the end then update it or is there a better more efficient way of doing it.

I’m sorry if i’m explaining this poorly it’s very late here and i’m tired. Any help wold be greatly appreciated.

Cheers.