Union

The Union operator combines elements from input relations. The Union operator captures one of every record in every relation and provides one of every record as output, with duplicates removed.

All input relations must have the same schema. Relations that are output from the Union operator will have the same schema.

Because the Union operator does not pass through duplicates, if two different files input to it indicate size of 1, the behavior is similar to having two single streams input to a merged file.

That is, for each event a new row is added, and one subtracted. Note that if the input files are identical (the rows are exactly the same), and the Tuple Size is also 1, then the previous output is deleted, but nothing is added.

To Create a Union Operator

1. Drag a Union operator from the Palette to the Design view.

2. Connect the input of the new Union component to two or more operators that have relation output.

3. Double-click the Union operator.

   The property editor opens. Notice that the component has inherited the schema of its input relations.

4. As needed, configure the following property: Name:

5. (Optional) Click the Documentation tab and supply notes on this component.

6. Click OK.