Using TDbColSetIter

TDbColSetIter provides a useful way to iterate over the contents of a column set. Given a CDbColSet* set, we can count the number of nullable columns like this:

TInt nullable=0;
for (TDbColSetIter iter(*set);iter;++iter)
    {
    if ((iter->iAttributes&TDbCol::ENotNull)==0)
        ++nullable;
    }