There are two mechanisms for creating user-defined functions in SQL Anywhere. You can use the SQL language to write the function, or you can use Java.
You can implement your own functions in SQL using the CREATE FUNCTION statement. The RETURN statement inside the CREATE FUNCTION statement determines the data type of the function.
Once a SQL user-defined function is created, it can be used anywhere a built-in function of the same data type is used.
For more information on creating SQL functions, see Using Procedures, Triggers, and Batches.
Java classes provide a more powerful and flexible way of implementing user-defined functions, with the additional advantage that they can be moved from the database server to a client application if desired.
Any class method of an installed Java class can be used as a user-defined function anywhere a built-in function of the same data type is used.
Instance methods are tied to particular instances of a class, and so have different behavior from standard user-defined functions.
For more information on creating Java classes, and on class methods, see Creating a class.