Examples of the use of "&where" with Ditto?

I’m trying to investigate whether or not it’s possible for Ditto to use info in a user-provided table when it is called on to provide tag-based category listings.

Can anyone point me to an example of how the "where" parameter is used? It would seem that it might have potential in this regard, but the examples I saw via a Google search suggest an assumption is made about what table is used. Is this correct or is there a way the argument to "where" can be twisted around to operate on a table that is still part of the MODx database, but provided by the user nonetheless?

Thanks,
Matt

"where" is for a type of filtering in the sql query; "WHERE id = 42" or WHERE pagetitle = ’Home’. It does not change the table being queried.