回显数组值的问题

I am having trouble echoing values from an array. I am using a mysql query to create an array, $online, containing the names of currently online users. Here is my code:

<?php
    $goodbye = time() - 300;
    $qry="SELECT UserName FROM Members WHERE Seen >=$goodbye";
    $result=mysql_query($qry);

    if($result) {
        $online = mysql_fetch_assoc($result);
        foreach($online as $u) {
            echo $u;
            echo "<br>";
        }
    } else {
        die("Query Failed");
    }
?>

When viewing this on my web page, only the first index of the array is shown (as in: if User1, User17, and User69 are all online, only User1 will appear on the list). I'm sure this is happening because I'm using echo incorrectly, but I haven't been able to figure it out yet. Any tips? Thanks.

You should loop it like (mysql_fetch_assoc)

if($result) {
    while ($row = mysql_fetch_assoc($result)) {
        echo $row["UserName"];
    }
}

Also, notice the Warning.