A SQL function is a program that performs an operation on data. SQL functions provide a powerful way to perform operations when retrieving data from a table. For example, you may need to display employee names in uppercase in a report. Or you may need to display employees' hire dates with the name of the month spelled out.

Many functions work on specific data types. Each value manipulated by the Oracle Database has a data type. Data types provide a way to define the behavior of data. When you create a table, you must specify a data type for each of its columns.