EasyMorph Help

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{{ transformations:SelectDbRowsAction.png}}
======SELECT MATCHING DATABASE ROWS======
Category: Import / Database\\

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=====Description=====
Selects rows from a database table where a combination of key fields matches a combination of key fields in an EasyMorph table. \\

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=====Use cases=====
This action can be used for //pre-filtering//. Pre-filtering means that instead of loading an entire dataset and then filtering it, only a few fields are loaded (using [[transformations:importsql|Import from database]]) that are necessary for filtering, as well as primary/foreign keys (i.e. IDs). When imported, these fields can be filtered by any of the various EasyMorph transformations. The resulting subset of IDs is used to fetch full records from the source dataset using the //Select matching database rows// action. Pre-filtering can be helpful when the source table is large and doesn't entirely fit in RAM.

Another use case is //cross-source filtering// which means importing database records having IDs that are obtained from another data source (e.g., text file or spreadsheet).\\

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=====Remarks=====
Under the hood, the action creates a series of SQL requests and combines their results into one table. The action doesn't create or modify data in the database and can work having only read-only access to the database.\\

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=====See also=====
  *[[transformations:importsql|Import from database]]