Union Transformation.

Chapter 26: UNION transformation:

• Active and Connected.
  Explanation of UNION being active transformation:

The only condition for a transformation to be active is its row number should not change. That is the row number of the row coming in and goin out should be same.In case of Union Tansformation it is changed as the row order changes. unlike joiner transformation, Union trnsformation does not block any source and keeps on taking rows from any of the sources randomly.Thus the row number changes and hence it is an active transformation.
• The Union transformation is a multiple input group transformation that you use to merge data from multiple pipelines or pipeline branches into one pipeline branch.
• Works similar to UNION ALL.
  Thus it does not remove duplicates.
• The Union transformation is developed using the Custom transformation.
• Guidelines for using Union Transformation:

1. You can create multiple input groups, but only one output group.
2. All input groups and the output group must have matching ports. The precision, datatype, and scale must be identical across all groups.
3. The Union transformation does not remove duplicate rows. To remove duplicate rows, you must add another transformation such as a Router or Filter transformation.
4. You cannot use a Sequence Generator or Update Strategy transformation upstream from a Union transformation.
5. The Union transformation does not generate transactions.

• Union Transformation Tabs:

1. Transformation tab. You can rename the transformation and add a description.
2. Properties tab. You can specify the tracing level.
3. Groups tab. You can create and delete input groups. The Designer displays groups you create on the Ports tab.
4. Group Ports tab. You can create and delete ports for the input groups. The Designer displays ports you create on the Ports tab.

Create input groups on the Groups tab, and create ports on the Group Ports tab.

• We can create one or more input groups on the Groups tab. The Designer creates one output group by default.

• We cannot edit or delete the output group.

• The Designer uses the port names you specify on the Group Ports tab for each input and output port, and it appends a number to make each port name in the transformation unique.

• The Ports tab displays the groups and ports you create. You cannot edit group and port information on the Ports tab. Use the Groups and Group Ports tab to edit groups and ports.

• The naming convention for Union transformations is UN_Tr a n s f o r m a t i o n N a m e .

• The Union transformation is a non-blocking multiple input group transformation.

• Care to be taken: what if a particular port in input is not connected. 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.

• How UNION transformation deals with transaction: 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.