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Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. It describes what Power Query query folding is, and why it’s important in your data model designs. Query folding is the ability for a Power Query query to generate folding paper napkins for easter single query statement to retrieve and transform source data. The Power Query mashup engine strives to achieve query folding whenever possible for reasons of efficiency.

Power Query query that can be folded. In fact, the Power BI Incremental Refresh configuration window will notify you of a warning should it determine that query folding for the table can’t be achieved. If it can’t be achieved, the goal of incremental refresh is defeated. Query folding may occur for an entire Power Query query, or for a subset of its steps. When query folding cannot be achieved—either partially or fully—the Power Query mashup engine must compensate by processing data transformations itself. This process can involve retrieving source query results, which for large datasets is very resource intensive and slow.

We recommend that you strive to achieve efficiency in your model designs by ensuring query folding occurs whenever possible. Sources that support folding Most data sources that have the concept of a query language support query folding. However, data sources like flat files, blobs, and web typically do not. Transformations that can achieve folding Relational data source transformations that can be query folded are those that can be written as a single SELECT statement. A SELECT statement can be constructed with appropriate WHERE, GROUP BY, and JOIN clauses. Generally, the following list describes transformations that can be query folded. Simple logic implies uncomplicated operations, possibly including the use of M functions that have equivalent functions in the SQL data source, like mathematic or text manipulation functions.