Primary Keys of Views¶
The primary key of a view is a column or a set of columns whose value is unique in this view. In Virtual DataPort, you can define the primary key of views. At runtime, clients can obtain the primary key definition of a view by invoking the appropriate methods of the JDBC and ODBC interfaces of the Server. Some business intelligence tools use this information to generate more efficient queries.
Primary keys are part of the RESTful architecture of the Denodo
Platform. They allow browsing across the associations of views (see
section Associations) by using the Denodo RESTful Web service (see
section RESTful Web Service) or executing navigational queries
SELECT_NAVIGATIONAL). See more about this in the section Navigational Queries of the VQL Guide.
Virtual DataPort does not enforce the primary key definitions so there is no guarantee that a column marked as primary key indeed has unique values. The responsibility of uniqueness relies on the data source.
To define the primary key of a base view, in the “Create view” or in the “Edit view” dialog, select the check box beside the type of the fields that form the primary key and click Set selected as PK. You will see that these fields are marked with the icon .
To remove the current definition of the primary key, clear all the check boxes and click Set selected as PK.
When creating a JDBC base view, the Server automatically sets the definition of the primary key of the view according to the definition of the selected table in the database.
When creating other types of base views, you have to define the primary key manually.
To define the primary key of a derived view, click the Output tab, select the check box beside the type of the fields that form the primary key and click on Set selected as PK. As in base views, these fields are marked with the icon .
The primary key definition of views is not propagated. That is, you have to define the primary key in the views where you need that information.