The Union transformation is a non-blocking multiple input group transformation. You can connect the input groups to different branches in a single pipeline or to different source pipelines.
When you add a Union transformation to a mapping, you must verify that you connect the same ports in all input groups. If you connect all ports in one input group, but do not connect a port in another input group, the Integration Service passes NULLs to the unconnected port.
The following figure shows a mapping with a Union transformation:
When a Union transformation in a mapping receives data from a single transaction generator, the Integration Service propagates transaction boundaries. When the transformation receives data from multiple transaction generators, the Integration Service drops all incoming transaction boundaries and outputs rows in an open transaction.