Union of PGX Frames
You can join two PgxFrames that have compatible columns (that is, same type and order).
opg4j> <firstFrame>.union(<secondFrame>).print()
<firstFrame>.union(<secondFrame>).print();
<first_frame>.union(<second_frame>).print()
The rows of the resulting PgxFrame are the union of the rows from the two original frames.
Note that the union operation does not remove duplicate rows that resulted by joining the two frames.