Question

I’m trying to do a MySQL Query that adds information to a database in a format that doesn’t overwrite it’s current value, but instead appends it as in the friends column would have friend1, friend 2, friend 3 … etc.

First I am unsure if INSERT INTO is right:

$username = $_SESSION['username'];

mysql_query("INSERT INTO members (friends) WHERE username = $username
    VALUES ('$friendtoadd')");

What I want to do is have this do two things

1) Add the friend in a format mentioned so that it can later be called out that if the $username set in session is active then the results posted on the page are only from those other users contained in their friends column.

2) If the $friendtoadd already exists in their column for friends then it does nothing.

Answer 1

UPDATE members SET friends = CONCAT_WS(', ', friends, '$friendtoadd') where username = '$username'

I hope $friendtoadd as well as $username are sanitized through mysql_real_escape_string

Also, this design isn’t very good. You should have a seperate friends table
so

table friend
id (auto increment), userID, name)

then do 
Insert into friend SET userID = $userID, name = '$friendName'