Column References 

A column reference represents the value of a column in a table. It may be either a column name or a column name qualified with a table name. If no table name is specified, the table to which the column belongs is implicit. In this case, the column name must be uniquely be determinable in the most local scope.

Syntax

<column reference> ::=                   <column name>                   | <table name> '.' <column name>. <column name> ::= <identifier>. <table name> ::= <identifier>.

Example

SELECT employee_name, epmloyees.epmloyee_id                FROM employees

Column References. Here employee_name  is a column name and epmloyees.epmloyee_id  is a qualified column name.

More Information

Identifiers