[Zope] optional sql tag

[Horvath Adam]

Hi,

I have 3 select -> there are 3 form variable: year, month, 
day
which are arguments for the ZSQL Method:

select * from table c
<dtml-sqlgroup where>
  ...
<dtml-and>
  c.date >= <dtml-sqlvar "year+'-'+month+'-'+day" 
type=string>
<dtml-and>
  ...
</dtml-sqlgroup>

It works great, but when there is nothing in the form 
variables,
it will be  c.date >='--'

How can I do that with empty form variables this <dtml-
and> tag
would be optional?
 
Halinux