Extending Informix Dynamic Server 2000 Extending an Operation

The database server provides special SQL-invoked functions, called built-in functions, that provide some basic mathematical operations.

Figure 6-4 shows the built-in functions that you can overload.

Built-In Functions That You Cannot Overload

The following table lists the built-in functions that you cannot overload.

Tip: Technically, CURRENT, DBSERVERNAME, SITENAME, TODAY, and USER, are not built-in functions, but built-in macros. You can register overloaded routines by those names, but you cannot use them in SQL statements.

The following table lists the built-in functions for the Optical Subsystem that you cannot overload.

The database server provides versions of the built-in functions that handle the built-in data types. You can write a new version of a built-in function to allow the function to operate on your new opaque data type. If you write a new version of a built-in function, follow these rules:

• The name of the built-in function must match the name that Figure 6-4 lists.The name is case insensitive; the abs() function is the same as the Abs() function.
• The built-in function must be one that you can overload.
• The built-in function must handle the correct number of parameters, and these parameters must be the correct data type.
• The built-in function must return the correct data type, where appropriate.

For more information on the built-in functions, see the Expression segment in the Informix Guide to SQL: Syntax.