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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).
Supply error messages and a user guide
Avoid database server exceptions
SQL restrictionsThe database server raises exceptions due to restrictions that the virtual-table interface (VTI) imposes on SQL.

SQL restrictions

The database server raises exceptions due to restrictions that the virtual-table interface (VTI) imposes on SQL.

A user cannot specify a dbspace in a CREATE TABLE or ALTER FRAGMENT statement. The VTI does not support the following statements for virtual tables:

An ALTER TABLE statement that adds, drops, or modifies a column
A LOCK TABLE or UNLOCK TABLE statement
An ATTACH or DETACH keyword in an ALTER FRAGMENT statement

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