help needed building query string based on which form fields that are filled.

Hi,   I've got a html form where not all fields need to be filled by the users. How can I build a MySQL query based on which fields the user have filled?   My guess is that I can do something like this:   if(!empty($f_name)) { some_commands_to_add_$f_name_to_querystring } if(!empty($l_name)) { some_commands_to_add_$f_name_to_querystring } some_commands_to_build_querystring_based_on_if's   $result = mysql_query($query)     But what commands/functions should I use to build the query? -- anders thoresson