Database Reference
In-Depth Information
Union transformation
The Union transformation is used to merge data from multiple sources. Union is a multiple
input, single output transformation. It is the opposite of router transformations, which we
discussed earlier. The basic criterion to use a Union transformation is that you should have
data with the matching data type. If you do not have data with the matching data type com-
ing from multiple sources, the Union transformation will not work. The Union transforma-
tion merges the data coming from multiple sources and does not remove duplicates, so it
acts as the union of all SQL statements.
As mentioned, union requires data to come from multiple sources. Union reads the data
concurrently from multiple sources and processes the data. You can use heterogeneous
sources to merge the data using a Union transformation.
A mapping indicating the Union transformation is shown in the following screenshot:
Working on Union transformation is a little different from other transformations. To create
a Union transformation, perform the following steps:
1. Once you create a Union transformation, drag all the required ports from one
source to the Union transformation. As soon you drag the port, the union creates an
input group and also creates another output group with the same ports as the input.
