Will changing the "transform sample file" query cause all dataflow data to be dropped?

[DotU]

I have a dataflow which reads ALL the excel files being saved to a SP Folder.

Each Excel file is standard: exactly same column names, etc.
The dataflow has incremental refresh, so it only reads new files from last 15 days and older data which has already been read stays as it is.

Over the span of a few months of saving our files in the dedicated location, we have successfully collected data from 800+files.

I need to update the helper query (transform sample file query) to make it more efficient. I will not be adding any new columns, the final schema will be the same as it is now. Will doing this cause all the data to be dropped and re-read? Or would the new (more efficient) transformation steps only be applied to future files?

If needed, I can share the queries if that would help to make the question more clear.

Many thanks!

[v-yadongf-msft]

Hi   @DotU 

"Transform sample file" query allows work in a group of files through just one function and make transformations in file combination automatically, which will refresh the dataflow and apply to all dataflow data.

When you apply "Transform sample file" query, it will ask you refresh dataflow.  If you refresh dataflow, it only refresh data and will not cause all the data to be dropped.

 

 

For details on transform sample file, please refer to the documentations:

Using custom functions in Power Query - Power Query | Microsoft Docs

Combine files (binaries) in Power BI Desktop - Power BI | Microsoft Docs

Best regards,

Yadong Fang

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