Does creating a base view from query mean the query can not be delegated?

Applies to: Denodo 7.0 , Denodo 6.0 , Denodo 5.5 , Denodo 5.0
Last modified on: 25 Sep 2018
Tags: View creation Performance ODBC data sources JDBC data sources

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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. 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.

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

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