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If you use the option "Create Base View from Query" to create a base view, any condition added when querying the view will be delegated to the data source if the condition is included in the SQL query using interpolation variables or if the special “WHEREEXPRESSION” interpolation variable is used in the query specification.

Another option to allow delegation to the data source when the data source is JDBC and the query used to create the base view is a SELECT statement is to modify the Wrapper Source configuration on the base view. After creating the base view go to the Advanced screen and then to Search Methods > Wrapper Source Configuration from the Virtual Dataport Administration Tool. Under Wrapper Source Configuration change the Delegate SQL sentence as subquery property to Yes and save the changes. By doing this, VDP will be able to delegate more queries over the base view to the database.

Note: Starting from Denodo 6.0, the property Delegate SQL sentence as subquery is set to ‘Yes’ by default.

If you have a base view created from query with a projection view that contains additional conditions or does not project all the base view fields, the message “Projection/Selection queries cannot be delegated to this database” means that Virtual DataPort will be responsible of performing these operations that can not be delegated them the database because of the base view query definition.

References

Virtual DataPort Administration Guide: Creating Base Views from SQL Queries(JDBC/ODBC) 

Virtual DataPort Administration Guide: Using the WHEREEXPRESSION Variable

Disclaimer
The information provided in the Denodo Knowledge Base is intended to assist our users in advanced uses of Denodo. Please note that the results from the application of processes and configurations detailed in these documents may vary depending on your specific environment. Use them at your own discretion.
For an official guide of supported features, please refer to the User Manuals. For questions on critical systems or complex environments we recommend you to contact your Denodo Customer Success Manager.

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