[Zope-DB] zsql optional parameters from a form

[David Salgado]

Hi there

I've got a form with an input text box called 'msisdn', and a ZSQL query 
like this;

<dtml-comment>
title: test
arguments: msisdn
connection_id: mydbconn
</dtml-comment>
select * from mytable
<dtml-sqlgroup where>
   <dtml-sqltest msisdn op=eq type=string optional>
</dtml-sqlgroup>

This works fine if I supply a MSISDN in the text box - I get the records 
I expect. But, if I leave msisdn blank, then from the trace log I can 
see that the query that gets sent to the mysql database is "select * 
from mytable where msisdn='' ", and so I get no records when what I want 
is ALL the records.

My optional 'msisdn' parameter is always being supplied, even if I leave 
the text box empty. Is there any way I can prevent this from happening?

Eventually, I want to have a form with lots of fields to specify a 
variety of criteria, but if blank text boxes are always coming through 
as empty strings, it's not going to work.

Thanks in advance for any help.

David