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Pentaho Documentation

Merge rows (diff)

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The Merge rows (diff) step compares and merges data within two rows of data. This step is useful for comparing data collected at two different times. For example, the source system of your data warehouse might not contain a timestamp of the last data update. You could use this step to compare the two data streams and and merge the dates and timestamps in the rows.

Based on keys for comparison, this step merges reference rows (previous data) with compare rows (new data) and creates merged output rows. A flag in the row indicates how the values were compared and merged. Flag values include:

  • identical

    The key was found in both rows, and the compared values are identical.

  • changed

    The key was found in both rows, but one or more compared values are different.

  • new

    The key was not found in the reference rows.

  • deleted

    The key was not found in the compare rows.

If the row's flag is identical or deleted, the merged output rows are based on the reference rows.

For new or changed rows, the merged output rows are based on the compare rows.

You can also send values from the merged and flagged rows to a subsequent step in your transformation, such as the Switch-Case step or the Synchronize after merge step. In the subsequent step, you can use the flag field generated by Merge rows (diff) to control updates/inserts/deletes on a target table.

Select an Engine

You can run the Merge rows (diff) step on the Pentaho engine or on the Spark engine. Depending on your selected engine, the transformation runs differently. Select one of the following options to view how to set up the Merge rows (diff) step for your selected engine.

For instructions on selecting an engine from your transformation, see Run configurations.