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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®.
Descriptor function referenceThese topics provide the syntax and usage for the functions that the HCL Informix® database server supplies to access-method developers.
Accessor functionsThe Virtual-Table Interface (VTI) library contains functions that primarily access selected fields from the various descriptors.
The mi_eval_am_qual() accessor functionThe mi_eval_am_qual() function evaluates parts of a qualification that the access method does not set to MI_VALUE_TRUE or MI_VALUE_FALSE.

The mi_eval_am_qual() accessor function

The mi_eval_am_qual() function evaluates parts of a qualification that the access method does not set to MI_VALUE_TRUE or MI_VALUE_FALSE.

Syntax

mi_boolean 
mi_eval_am_qual(MI_ROW *row, MI_AM_QUAL_DESC *qualDesc);

row: Points to the row structure.
qualDesc: Points to the qualification descriptor.

Usage

The am_getnext purpose function can call mi_eval_am_qual() to obtain results for any qualifications that the access method cannot complete. Before the access method can call mi_eval_am_qual(), it must call mi_row_create() to assemble a row.

Tip: Both mi_row_create() and mi_eval_am_qual() can increase response time and CPU usage. Call them only if necessary.

If mi_eval_am_qual() returns MI_TRUE, am_getnext returns MI_ROWS. If mi_eval_am_qual() returns MI_FALSE, am_getnext disregards the current row, does not return a value, and starts to evaluate the next row.

Return values

MI_TRUE: Indicates that the row qualifies.
MI_FALSE: Indicates that the row does not qualify.

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