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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.
DataBlade® API Programmer's GuideThe Informix® DataBlade® API Programmer's Guide describes information about the DataBlade® API, the C-language application programming interface (API) provided with HCL Informix®.
Create user-defined routines
Extend data typesThis section describes the ways to extend data types with C user-defined routines (UDRs).
Provide statistics data for a columnThe database server can provide statistics data for the columns of a table. This statistics data describes the distribution of the values within a column. The query optimizer uses this statistics data to determine the best path for an SQL statement. With this information, the optimizer can estimate the effect of a WHERE clause by examining, for each column included in the WHERE clause, the proportionate occurrence of data values contained in the column.
Collect statistics dataThe UPDATE STATISTICS statement collects statistics about the tables in your database. It automatically collects statistics for all columns with built-in data types (except TEXT and BYTE). However, it cannot automatically collect statistics for columns with user-defined data types because it does not know the structure of these data types.
Collect the statisticsThe statcollect() user-defined function is an iterator function; that is, the database server calls statcollect() for each of the rows on whose column of a user-defined data type UPDATE STATISTICS is collecting statistics. As with other iterator functions, the database server uses an iterator-status constant to indicate when the statistics-collection function is called.
SET_INIT in statcollect()When the iterator-status constant is SET_INIT, the database server has invoked the initial call to statcollect(). Usually, in this initial call, your statcollect() function allocates and initializes an internal C structure, called a statistics-collection structure. The statistics-collection structure is a holding area for the statistics data that statcollect() gathers on a row-by-row basis.

SET_INIT in statcollect()

When the iterator-status constant is SET_INIT, the database server has invoked the initial call to statcollect(). Usually, in this initial call, your statcollect() function allocates and initializes an internal C structure, called a statistics-collection structure. The statistics-collection structure is a holding area for the statistics data that statcollect() gathers on a row-by-row basis.

Take the following actions:

Define your a statistics-collection structure to hold statistics data.
Allocate and initialize this statistics-collection structure within the SET_INIT case of your statcollect() function.

Your statcollect() function can use the MI_FPARAM structure to store this statistics-collection structure (and any other state information) between iterations of statcollect(). Allocate any memory used across multiple iterations of statcollect() from the PER_COMMAND pool and free it as soon as possible. Allocate any memory not used across multiple invocations of statcollect() from the PER_ROUTINE memory pool.

Use the mi_fp_setfuncstate() function to save a pointer to the user-state memory in the MI_FPARAM structure of your statcollect() function. For more information, see Saving a user state.

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