Data which is loaded to internal strage

[taimaizumi]

Hi, community!

I have on question about data loaded to internal strage after editing source data at "Power query"

I usually filter out some records or columns at "Power query", which resulting in showing only data which is not filtered out.

But I wonder in which order above process is done.

1. First loaded to data to internal strage and then filter out records
2. First filter out records and then loaded to internal strage

The background for this question is that if pattern 2 is the case, data which is deployed into DWH should not be filtered out in advance because power BI user can do it without using big local memory, and it will lead to save time to prepare data for users.

Thanks in advance!

[taimaizumi]

@v-zhangti 
Thank you for your response!
I checked your link and could understand outline about how power query get data from data source.

If my transformation can be folded (which means my transformation can be written by SQL?), basically all transformation is done on data source side and power query just get result of that.
If not, power query has to get all(or subset) data first and then transform it on power query side(=internal strage)

Is my above understanding correct?

[v-zhangti]

Hi, @taimaizumi 

Power query works closer to the second one.

The steps you specify (such as rename a table, transform a data type, or delete a column) are recorded by Power Query Editor. Each time this query connects to the data source, Power Query Editor carries out those steps so that the data is always shaped the way you specify. This process occurs whenever you use Power Query Editor, or for anyone who uses your shared query, such as on the Power BI service. 

Tutorial: Shape and combine data in Power BI Desktop - Power BI | Microsoft Learn

Understanding query evaluation and query folding in Power Query - Power Query | Microsoft Learn

Best Regards,

Community Support Team _Charlotte

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