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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
Determine required aggregate support functions
Return an aggregate result different from the aggregate state

Return an aggregate result different from the aggregate state

The aggregate result is the value that the user-defined aggregate returns to the calling SQL statement. If the user-defined aggregate does not include a FINAL support function, the database server returns the final aggregate state; that is, it returns the value of the aggregate state after the last aggregate iteration. However, if your UDA needs to return a value whose data type is different from the aggregate state, use a FINAL support function to convert the final aggregate state to the data type that you want to return from the aggregate.

For example, the PERCENT_GTR user-defined aggregate (see The PERCENT_GTR user-defined aggregate) returns the percentage of values greater than some value as a percentage; that is, as a fixed-point number in the range 0.00 to 100.00. To handle integer values, the user-defined aggregate would require an aggregate state that holds the following values:

The total number of aggregate arguments greater than 10
The total number of aggregate arguments
The value to compare against

However, the aggregate result of PERCENT_GTR is a fixed-point number. Therefore, you would not want the aggregate to return the final state to the calling SQL statement. Instead, the FINAL support function needs to perform the following steps:

Divide the total number of arguments that are greater than 10 by the total number of arguments and multiply by 100.
Return the fixed-point quotient, which is the percentage of values greater than 10.

For the complete example of the PERCENT_GTR user-defined aggregate, see The PERCENT_GTR user-defined aggregate.

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