SQLite::VirtualTable::Pivot::Cursor - a cursor for a pivot table query
Objects in this class represent cursors for queries on pivot tables.
They maintatin a statement handle corresponding to an unpivotted query on the base table. The pivotting operation is done one row at a time, as data is returned; i.e. we order by the id, and group on the fly.
It must be possible for multiple cursors to exist at once on the same pivot table, in case it occurs more than once in a query.