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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-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.
Descriptor function reference
Accessor functionsThe Virtual-Index Interface (VII) library contains functions that primarily access selected fields from the various descriptors.
The mi_qual_boolop() accessor functionThe mi_qual_boolop() function retrieves the Boolean operator that combines two qualifications in a complex expression.

The mi_qual_boolop() accessor function

The mi_qual_boolop() function retrieves the Boolean operator that combines two qualifications in a complex expression.

Syntax

MI_AM_BOOLOP mi_qual_boolop(MI_AM_QUAL_DESC *qualDesc);

qualDesc: Points to the qualification descriptor.

Usage

The access method first obtains results for the simple functions in a complex qualification. To determine how to combine the results that the access method has so far, it can call the mi_qual_boolop() function.

Important: The database server has no means to detect if a secondary access method does not set values for complex expressions.

If the access method has no code to evaluate AND or OR, the am_scancost purpose function can take the following precautions:

Call mi_qual_boolop().
If mi_qual_boolop() indicates the presence of an AND or OR operator, return a negative value from am_scancost to ensure that the optimizer does not use the access method to process the query.

Return values

MI_BOOLOP_NONE: Indicates that the current qualification does not contain a Boolean operator.
MI_BOOLOP_AND: Indicates that the current qualification contains a Boolean AND operator.
MI_BOOLOP_OR: Indicates that the current qualification contains a Boolean OR operator.

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