Home
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-Index Interface GuideThe Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix® typically with a DataBlade® module.
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-index interface (VII).
Process queries that involve a virtual indexThis section describes various options for processing a SELECT statement, or query, that involves a virtual index.
Interpret the scan descriptorThe database server constructs a scan descriptor in response to a SELECT statement. The scan descriptor provides information about the key data types and the locks and isolation levels that apply to the data that the query specifies.

Interpret the scan descriptor

The database server constructs a scan descriptor in response to a SELECT statement. The scan descriptor provides information about the key data types and the locks and isolation levels that apply to the data that the query specifies.

As one of its primary functions, the scan descriptor stores a pointer to another opaque structure, the qualification descriptor that contains WHERE-clause information. To access the qualification descriptor, use the pointer that the mi_scan_quals() function returns. A NULL-valued pointer indicates that the database server did not construct a qualification descriptor.

Important: If mi_scan_quals() returns a NULL-valued pointer, the access method must format and return all possible rows.

Rate this topic

5 stars 4 stars 3 stars 2 stars 1 star

Comment on this topic.

By clicking this box, you acknowledge that you are NOT a U.S. Federal Government employee or agency, nor are you submitting information with respect to or on behalf of one. HCL provides software and services to U.S. Federal Government customers through its partners immixGroup, Inc. Contact this team at https://hcltechsw.com/resources/us-government-contact. Do not include any personal data in this Comment box.