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.

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.

Functions are similar to procedures. Deciding whether to create a function or a procedure depends on what you want returned, and the object will be called. When deciding whether to create a UDF or a procedure, consider their unique characteristics listed below.

Functions:

Procedures:

• CREATE FUNCTION statement
• Creating a class
• Stored procedures, triggers, batches, and user defined functions