The NLS_NUMERIC_CHARACTERS option specifies the decimal marker (of decimal separator) and thousands group marker (of group separator) for the session.
The NLS_NUMERIC_CHARACTERS is a result of the NLS_LANG setting.
The decimal character and the group separator must be two different single-byte characters, and cannot be a numeric value or any of the following characters: plus sign (“+”), less-than sign (“<”), minus sign or hyphen (“-” ), or greater-than sign (“>”).
If the decimal character is not a period (.), you must use single quotation marks to enclose all number values that appear in expressions in your SQL statements.
NLS_NUMERIC_CHARACTERS affects the display of numeric data.
Within a session, you can dynamically modify the value by using the SQL statement
ALTER SESSION SET NLS_NUMERIC_CHARACTERS = option-value
Changing the Decimal Marker to a Comma
The following statement changes the decimal marker to a comma, and the thousands marker to a space.
ALTER SESSION SET NLS_NUMERIC_CHARACTERS = ', '
The result of 1234.56 is now 1 234,56.