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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
Create special-purpose UDRsThis section describes how to create special UDRs, such as iterator functions, user-defined aggregates, and optimization functions.
Write an aggregate functionAn aggregate is a function that returns one value for a group of queried rows. The aggregate function performs one iteration for each of the queried rows.
Creating a user-defined aggregate
Implementing a user-defined aggregate function with C user-defined functions

Implementing a user-defined aggregate function with C user-defined functions

About this task

To implement a user-defined aggregate function with C user-defined functions:

Procedure

Determine the content and data type of the aggregate state.
Write the C UDRs that implement the required aggregate support functions for the data type on which you want to implement the user-defined aggregate.
Define the user-defined aggregate in the database with the CREATE AGGREGATE and CREATE FUNCTION statements.

Results

After you complete these steps, you can use the aggregate in an SQL statement.

The following sections describe each of these development steps in more detail and use the SQSUM1 user-defined aggregate (which A sample user-defined aggregate describes) as an example.

Table 1. A sample user-defined aggregate
User-Defined Aggregate	Description	Definition
SQSUM1	Sums all values and calculates the square of this sum	(x₁ + x₂ + x₃ + ... )²

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