Row Numbers in Azure Data Factory Data Flows

(2020-Oct-05Adding a row number to your dataset could a trivial task. Both ANSI and Spark SQL have the row_number() window function that can enrich your data with a unique number for your whole or partitioned data recordset. 

Recently I had a case of creating a data flow in Azure Data Factory (ADF) where there was a need to add a row number.

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Instant reaction was to this new additional row number column using a derived column transformation - However, this was my mistake and ADF notified me that rowNumber() -  data flow function was only available in the Windows transformations -

OK, I moved on and added a Window Transformation task, which does require at least one sorting column.

However, this was a bit of an issue in my data case. I didn’t need to sort and change the order of my recordset. Transformed dataset needed to be in the same order as its original sourcing data, as it would help to locate a transformed data record with its sourcing sibling record with the help of the new Row Number column.

So I thought that it wouldn't hurt to add just a static constant value column (let’s say with value  = 1 ) and then use this new (1) valued column in my rowNumber() window transformation as a sorting attribute. 

1) First I added a Derived Column transformation with the Column_Value_1 column value set to 1 (or any other constant value of your preference).
2) Then I added a Window transformation with the rowNumber() function and Column_Value_1 as a sorting column.
3) Then I was able to see my output result with preserved order of records and additional Row Number column.

Joseph Edwards has just pointed out that using the Surrogate Key transformation would achieve the very same result of adding a row number column, and this step doesn't even require sorting columns. I've just tested, and it's working, amazing! I have written this whole blog post just to realize that there is a better way to number rows in the Azure Data Factory flows :-)