# Add sequence

The Add sequence step adds a sequence to the PDI stream. A sequence is an ever-changing integer value with a specific start and increment value. You can either use a database sequence to determine the value of the sequence, or have it generated by PDI. PDI-generated sequence values are unique when used in the same transformation, and return to the same starting value each time you run the transformation.

The following transformation steps may also be useful when working with sequences:

* [**Add value fields changing sequence**](https://wiki.pentaho.com/display/EAI/Add+value+fields+changing+sequence)

  Adds a sequence when the values of a field change. Each time a value of at least one field changes, the added sequence resets to its starting point.
* [**Group By**](/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview/group-by-landing-page-article.md)

  Builds aggregates by grouping and generates sequential numbers within rows with repeating values.

See the [Get ID from Slave Server](https://wiki.pentaho.com/display/EAI/Get+ID+from+Slave+Server) step if you need a unique ID in a clustered environment.


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