You should really use a seperate table for subscriptions. Index it by user_id as this is a write-little read-many type table. Ultimately I'd look to do something like...

User_table

user_id
password
Name
Email
...

Mailinglist_table

Maillist_id
Name
...

Subscription_table

Maillist_id
User_id

Admin_priv_table

user_id
Maillist_id

selecting and displaying a user's profile would be something like.

$uid #contains usersid
($uname, $upass, $uemail) = $dbi->fetchrow_result("select User_ID, Nam
+e, Password, Email from User_Table where User_ID = '$uid'");
#output basic info

$sth = $dbi->prepare("select MailListName from Mailinglist_table, Subs
+cription_table where Subscription_table.MaillistID = MaillingList_tab
+le.MaillistID  AND Subscription_table.User_ID = '$uid')
$sth->execute;
while (($subname) = $sth->fetch_row_array) {
    #OUtput MaiList Name
}
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