A Union stage is used to combine multiple datasets
with identical sets of column headers to produce a single output. Because the
headers are the same in each source file the rows can be stacked on top of each
other to produce a single unified dataset.
If there are unmatching columns in the source schemas
they will be included in the output dataset, but only the rows from the source
of the unmatched column will be populated.
To union datasets:
Insert a union stage
Select inputs with matching header schemas
A single unioned dataset will be output