Descriptors

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Descriptors

The application programming interface (API) that the IBM Informix database server provides with the VTI consists primarily of the following components:

Opaque data structures, called descriptors, that the database server passes by reference to purpose functions
Accessor functions that store and retrieve descriptor values

The Virtual-Table Interface (VTI) provides the following descriptors and accessor functions.

Descriptor	Describes	Accessor- Function Prefix	Reference
qualification descriptor (MI_AM_QUAL_DESC)	WHERE clause criteria	mi_qual_	Qualification Descriptor
row descriptor (MI_ROW)	Order and data types of projected columns	Various DataBlade API functions	IBM Informix: DataBlade API Programmer's Guide
scan descriptor (MI_AM_SCAN_DESC)	SELECT clause projection	mi_scan_	Scan Descriptor
statistics descriptor (MI_AM_TSTATS_DESC)	Distribution of values	mi_tstats_	Statistics Descriptor
table descriptor (MI_AM_TABLE_DESC)	Table attributes and fragment partition	mi_tab_	Table Descriptor

Each of the following sections describes the contents of a descriptor and the name of the accessor function that retrieves each descriptor field. For complete syntax, including the parameters and return type of each accessor function, refer to Accessor Functions.

Important:

Because the internal structure of any VTI descriptor might change, IBM Informix declares them as opaque structures. To make a portable access method, always use the access functions to extract or set descriptor values. Do not access descriptor fields directly.