The NLS_CHARSET_ID function returns the character set identification number corresponding to a specified character set name.
See also:
NLS_CHARSET_NAMEINTEGER when you specify a valid value for the name of the character set, a number; otherwise NA.
A VARCHAR2 text expression that is a valid character set name or one of the following values:
CHAR_CS which specifies that the function return the database character set identification number of the server.
NCHAR_CS which specifies that the function return the national character set id number of the server.
See:
Oracle Database Globalization Support Guide for a list of character set names.