Error codes from 'mysql_error()'

I do an insert using phpadmin, and i get back the error message (or maybe it's a warning?) The insert is of a duplicate on a unique field. I expected an error, but when I do mysql_error() or mysql_errno(), nothing comes back(and I do it the next line in the script). the 'mysql_query($sql, $link)' function DOES insert when the value is unique, DOES return false, but I'd like to inform the user what the error was. PHP Admin can get the 'error' why can't I? Please reply to me as well, OK? I'm trying to finish this script at work today. gearond@oit.edu