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Extending Informix®Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix® includes many built-in extensions that are fully integrated in the database server. Informix® also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix®.
Creating extensionsYou can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
Virtual-Table Interface GuideThe Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix® tables and to data that does not conform to the storage scheme of HCL Informix®.
Design decisionsThese topics present the choices that you make to optimize the performance and flexibility of the access method that you can create with the virtual-table interface (VTI).
Process queries that involve a virtual tableThis section describes various options for processing a SELECT statement, or query, that involves a virtual table.
Qualifying data
Qualification by the database server

Qualification by the database server

The optimizer does not create a qualification descriptor if the cost for the access method to qualify rows exceeds the cost for a full table scan. If the database server does not construct a qualification descriptor, the mi_scan_quals() function returns a NULL-valued pointer.

Important: The mi_scan_quals() function returns a NULL-valued pointer to indicate that a qualification descriptor does not exist. In response to the NULL-valued pointer, the access method creates a row from each source record.

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