Inserts, Updates and Deletes Over Views¶
DELETE statements allow respectively
inserting, updating and deleting rows from a view. These statements
modify the data stored in the underlying data source.
However, as in any database management system, there are limitations on the views that can be updated.
A base view created over one of the following types of data sources may be updateable:
JDBC data sources
ODBC data sources
Custom wrappers that were developed to be updateable
Base views created over a different type of data source are not updateable.
JDBC and ODBC base views from query are not updateable.
Virtual DataPort decides if a view is updateable or not following the rules of the SQL 92 standard. The main restrictions are:
SELECTstatement used in the definition of the view cannot have the clauses
FROMclause of the definition of the view can only refer to one view. Therefore, join, union, minus and intersect views are not updateable.
Flatten views are not updateable.
The value of the derived fields of views cannot be updated.
Views using aggregation functions are not updateable even if there is not
Join views are not updateable.
A union view is updateable only if all the following conditions are met:
The union view is a partitioned union (the section Removing Redundant Branches of Queries (Partitioned Unions) of the Administration Guide explains what a partitioned union is).
The feature “automatic simplification of queries” is enabled.
WHEREcondition of the
UPDATEstatement allows the optimizer to remove all the branches of the execution plan except one.
And, the view left in place in the execution plan is updateable.
A view with input parameters is updateable if you provide the value of these parameters in the
WHEREclause of the
A derived view is not updateable if its underlying view is not updateable.
In addition to the restrictions imposed by the standard, there are others:
Views involving a Denodo stored procedure are not updateable.
JDBC base views created over a stored procedure of a database are not updateable.
DF, JSON and XML base views are not updateable.
Although JDBC and ODBC base views are updateable, the base views created over a SQL query are not.
Base views over custom wrappers are updateable if they implement the methods described in the Developer Guide.