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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.
User-defined statistics
Display statistics dataThe dbschema utility with its -hd option displays statistics data for tables in your database. It can automatically display statistics for all columns with built-in data types (except TEXT and BYTE). It cannot automatically collect statistics for columns with user-defined data types because it does not know the structure of these data types.

Display statistics data

The dbschema utility with its -hd option displays statistics data for tables in your database. It can automatically display statistics for all columns with built-in data types (except TEXT and BYTE). It cannot automatically collect statistics for columns with user-defined data types because it does not know the structure of these data types.

For dbschema -hd to display statistics for a column with a user-defined data type, you must write a user-defined function named statprint() that generates text output of the statistics collected for your user-defined data type. The dbschema -hd command obtains the user-defined statistics from the encdat column of the sysdistrib system catalog table. The encdat column stores the statistics data in the stat opaque type. Therefore, dbschema must call the statprint() function for your user-defined data type to convert the statistics data from the stat data type to an LVARCHAR value that can be displayed.

To provide display statistics for your user-defined data type, you must:

Define a C statistics-display function to implement the statistics display.
Convert the user-defined statistics for the column to text output within statistics-display function.
Register this C function as a statprint() user-defined function.

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