added NoSuchObjectError
Added repr to field filter; added some comments
added is_compatible(); can_compose(); shared_representations(); row list object now accepts list-like appendable data
added autocommit to insert from select; add default lenght for dialects that require id; added records representation to SQL objects
ported xlrd streams
added as_records helper; distinct (as in SQL DISTINCT); renamed original distinct to unique(); sample accepts discard flag
Added execution context to the node evaluation call
more transformations
ported distinct and sample nodes; added tests; various fixes and improvements
added transformation tests
added distill_measure_aggregates()
reimplemented aggregate (still naive python implementation)