List the uses of a function and identify correct syntax.
A function is a set of PL/SQL code that is stored with a name inside the database. Like other objects created in the database, a function is created and owned by an Oracle user. Once created, it can be executed the same way that Oracle's built-in functions are executed: by calling it by name within a query or some other SQL or PL/SQL statement. A function usually accepts one or more parameters and always returns a value.

A stored function is one that is stored as a named object in the database. One advantage of using a stored function is that the function is executed within the server as opposed to executed within the client. The function can take advantage of higher processing power and of local access to additional data within the server.

Functions can be defined independently within a PL/SQL block without being stored inside the database. These kinds of functions are used in applications and might be executed on the client side. The stored functions we are discussing in this module, however, are much more common--they are stored within the database itself, which makes them reusable and shareable.

Functions are commonly used to:

1. Perform complex calculations and return the results
2. Accept an unformatted data field and return it in a standard format, such as a Social Security Number
3. Accept a key field and return summarized data from related tables

Functions can be used in SQL commands just about anywhere you can use an expression. For example, you can use them within the SET clause of an INSERT command, or within the SELECT or WHERE clauses of a query.

There are some restrictions in using and coding stored functions.
The following table shows the capabilities and restrictions of stored functions.

The next lesson explains the proper syntax for creating a stored function.