PL/SQL Built-in Functions
In addition to SQL commands, PL/SQL supports most SQL built-in functions.
These built-in functions are actually part of a PL/SQL package called STANDARD.
This package, owned by the user SYS, groups the functions together for easier
maintenance and use. If the structure of the function is ever needed, simply do a
DESC STANDARD and all parameter names and data types are displayed.
click on the following links to read more
Character Functions
Date Functions
Conversion Functions
Error Functions
Miscellaneous Functions