Hi, @Anonymous
For DirectQuery, each DirectQuery storage mode table must be based on a Power Query query that can be folded.
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. It can also contain column expressions (calculations) that use common built-in functions supported by SQL databases.
Generally, the following list describes transformations that can be query folded.
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Removing columns.
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Renaming columns (SELECT column aliases).
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Filtering rows, with static values or Power Query parameters (WHERE clause predicates).
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Grouping and summarizing (GROUP BY clause).
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Expanding record columns (source foreign key columns) to achieve a join of two source tables (JOIN clause).
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Non-fuzzy merging of fold-able queries based on the same source (JOIN clause).
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Appending fold-able queries based on the same source (UNION ALL operator).
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Adding custom columns with simple logic (SELECT column expressions). 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. For example, the following expressions returns the year component of the OrderDate column value (to return a numeric value).
- Pivoting and unpivoting (PIVOT and UNPIVOT operators).
For further information, you may refer to the following document.
Power Query query folding
Best Regards
Allan
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