SSIS Tutorials - Union All Transformation | Combine data from multiple sources

In this tutorial, we will learn " How to combine data from multiple homogeneous or heterogeneous source" by using Union All Transformation in your SSIS Package. 

The Union All transformation combines multiple inputs into one output. For example, the outputs from five different Flat File sources can be inputs to the Union All transformation and combined into one output.

The transformation inputs are added to the transformation output one after the other; no reordering of rows occurs. If the package requires a sorted output, you should use the Merge transformation instead of the Union All transformation. 

Union All Transformation in SSIS does not follow any particular order while merging the data and storing in the destination table. Supports multiple unsorted inputs and duplicate records can be possible in the final output file. It does have any error output. 

If the mapped columns contain string data and the output column is shorter in length than the input column, the output column is automatically increased in length to contain the input column. Input columns that are not mapped to output columns are set to null values in the output columns.

Used Components -

1. Data Flow Task

2. Source Assistants - Flat File, Csv file and SQL Server

3. Merge Join Transformation : Merge the sorted inputs

4. Sort Transformation : To Sort the data and remove duplicates

5. Row Sampling: To watch the final output

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Note: Combine the data from multiple sources, then there are more chances to having the duplicates in the final output. Hence, to remove duplicates,  one should combine a “UNION ALL” component with a “SORT” component. Because SORT Component provides an option to remove the duplicate rows and achieves the same thing as “UNION” query does in SQL.