Undefined index

[newbie93]

Hi, so this issue has been driving me crazy for the entire workday. I hope someone can help; I am sure it is trivial.
I am trying to access a user in a database based on their id. The id is auto incremented and thus unknown to the person accessing the user. I have created the functions below for accessing user information:

    function get_user_by_id($user) {
        global $connection;
        $query = "SELECT * ";
        $query .= "FROM person ";
        $query .= "WHERE personid=" . $user['id'] ." ";
        $query .= "LIMIT 1";
        $result_set = mysql_query($query, $connection);
        confirm_query($result_set);
        if ($user = mysql_fetch_array($result_set)) {
            return $user;
        } else {
            return NULL;
        }
    }
 
And the function below uses the one above. 
    function find_selected_user() {
        global $user;
        if (isset($_GET['id'])) { 
        //get all info for user in database
            $user = get_user_by_id($_GET['personid']);
        } else {
        //user doesn't exist in database -- return null? 
            $user = NULL; 
        }
    }. 
 

However, whenever I make an edit to the user, it does not make any sort of change to the database (the code for updating is not shown -- I think (*hope) the error is in the code above though).
Does anyone know why the user is not being updated? (I am assuming it is because the user is not even accessed).
Any help would be greatly appreciated!
Please let me know if I can clarify/elaborate on the question

[Rabbit]

Have you output the SQL string to see if it's being created correctly?

It's probably because on line 5, your $user variable, isn't an array, it's not going to have an id index.

[newbie93]

@Rabbit
Oh, I didn't realise that. I had assumed it was an array consisting of all the information in the database corresponding to the selected user. Is there a way I can make the user's information into an array? Thanks for your help!

[Rabbit]

You're thinking about the wrong thing. I'm talking about the $user variable that's being passed to the SQL. You're talking about what's being retrieved from the database. We're not even at that part yet.

I'm talking about line number 5, before anything even happens with the database, you're trying to access an index named id from the variable $user. That variable is just a string, the string that you passed into the function. The string that you pulled from the $_GET array with the index personid.