nested subselects are allowed

> > >         select *
> > >         from tabA
> > >         where col1 = (select col2
> > >                       from tabB
> > >                       where tabA.col3 = tabB.col4
> > >                       and exists (select *
> > >                                   from tabC
> > >                                   where tabB.colX = tabC.colX and
> > >                                         tabC.colY = tabA.col2)
> > >                      )

I checked this in Informix, it works.

Andreas