PL/SQL User's Guide and Reference

Package STANDARD

A package named STANDARD defines the PL/SQL environment. The package specification globally declares types, exceptions, and subprograms, which are available automatically to every PL/SQL program. For example, package STANDARD declares the following built-in function named ABS, which returns the absolute value of its argument:

FUNCTION ABS (n NUMBER) RETURN NUMBER;

The contents of package STANDARD are directly visible to applications. So, you can call ABS from a database trigger, a stored subprogram, an Oracle Precompiler application, an OCI application, and various Oracle tools including Oracle Forms, Oracle Reports, and SQL*Plus.

If you redeclare ABS in a PL/SQL program, your local declaration overrides the global declaration. However, you can still call the built-in function by using dot notation, as follows:

... STANDARD.ABS(x) ...

Most built-in functions are overloaded. For example, package STANDARD contains the following declarations:

FUNCTION TO_CHAR (right DATE) RETURN VARCHAR2;
FUNCTION TO_CHAR (left NUMBER) RETURN VARCHAR2;
FUNCTION TO_CHAR (left DATE, right VARCHAR2) RETURN VARCHAR2;
FUNCTION TO_CHAR (left NUMBER, right VARCHAR2) RETURN VARCHAR2;

PL/SQL resolves a call to TO_CHAR by matching the number and datatypes of the formal and actual parameters.