[Zope] sqlgroup

Hi, Is there a reason why the attribute 'having' doesn't exists? I want to use <dtml-sqlgroup having> <dtml-sqltest ... optional> </dtml-sqlgroup> this way when the sql-test tag contains nothing, also the having clause is not attached to the query. Why does 'where' exists and 'having' not? Is there another way to mimic 'having'? Thanks, Tom.