First step to support 'union' ResultSets.  The next step is to actually use the union feature when writing parts.
First step to support 'union' ResultSets.  The next step is to actually
use the union feature when writing parts.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb