A Union transformation has multiple input groups and one output group. You can create one or more input groups. The Developer tool creates one output group. You cannot create, edit, or delete the output group. Each group must have matching ports.

To create ports, you can copy ports from a transformation, or you can manually create them. When you create ports, the Developer tool creates input ports in each input group and output ports in the output group. The Developer tool uses the output port names you specify for each input and output port. The Developer tool also uses the same metadata for each port, such as datatype, precision, and scale.

You can connect the input groups from different branches in a single pipeline or from 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 a port in one input group, but do not connect the same port in another input group, the Data Integration Service passes NULLs to the unconnected port.