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.
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_RETONE in statcollect()For each row of a table, the statcollect() function collects the statistics data for the column that has the user-defined data type. When the iterator-status constant is SET_RETONE, the database server has invoked the statcollect() function on a single row of the table on which statistics is being gathered. At this point, statcollect() reads the column value from the first argument and places it into the statistics-collection structure.

SET_RETONE in statcollect()

For each row of a table, the statcollect() function collects the statistics data for the column that has the user-defined data type. When the iterator-status constant is SET_RETONE, the database server has invoked the statcollect() function on a single row of the table on which statistics is being gathered. At this point, statcollect() reads the column value from the first argument and places it into the statistics-collection structure.

The statcollect() function processes the statistics on a row-by-row basis; that is, for each iterator status of SET_RETONE, statcollect() merges the current column value into the statistics data in the internal statistics-collection structure. Therefore, the statcollect() function must perform the following tasks:

Obtain the address of the statistics-collection structure from the user state of the MI_FPARAM structure with the mi_fp_funcstate() function.
Compare the current column value with the current maximum and minimum values (if maximum and minimum are desired).
Merge the current column value into the distribution data in the statistics-collection structure.
Handle a NULL column value as appropriate for your distribution.

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.