A column’s default display name is its column name in the table definition.
You can use the AS clause to create a column alias name.
A column alias is an alternate name that you have picked for the displayed result.
An alias name can be used to give a name to a derived column, such as an expression or a column function.
An alias name does not change the name of a column in a table.

SELECT column1 AS alias1,
       column2 AS alias2, ...
  FROM table1, table2, ...;

> A column alias immediately follows the column name in the SELECT clause.
> A column alias does not change the column name in the table definition.
It only changes the result table and exists only for the duration of the statement.
> Oracle and DB2 display unquoted column names and aliases in uppercase.
> When the default name is displayed, underscores are replaced with spaces in some RDBMS systems such as DB2.
> If the alias is a single word with only letters, digits, and underscores, and it is not a reserved word, you do not need quotes.
> If the alias name contains spaces, special characters, or punctuation, enclose the alias in single or double quotes.
> You should make a habit of using quotes around alias names, just for consistency and partability to other RDBMS systems.
> With Access and PostgreSQL, AS is required. With others, is is optional.
But it should always be included when adding an alias name for portability.
> Oracle’s SQL*Plus command line processor truncates column aliases to the number of characters in the table’s column definition. DECIMAL(3) ‘PERCENT’ becomes ‘PER’.