What is national character set / NLS_NCHAR_CHARACTERSET?

• The national character set is the character set which is defined in oracle database in addition to normal character set.

• The normal character set is defined by the parameter NLS_CHARACTERSET and the national character set is defined by the parameter NLS_NCHAR_CHARACTERSET.

• The national character set is used for data stored in NCHAR, NVARCHAR2 and NCLOB columns while the normal character set is used for data stored in CHAR, VARCHAR2, CLOB columns.

• You can get the value of national character set or NLS_NCHAR_CHARACTERSET by,

SQL> select value from nls_database_parameters where parameter='NLS_NCHAR_CHARACTERSET';

VALUE
----------------------------------------
AL16UTF16

SQL> select value$ from sys.props$ where name='NLS_NCHAR_CHARACTERSET';

VALUE$
--------------------------------------------------------------------------------
AL16UTF16

SQL> select property_value from database_properties where property_name
='NLS_NCHAR_CHARACTERSET';

PROPERTY_VALUE
--------------------------------------------------------------------------------
AL16UTF16

• NLS_NCHAR_CHARACTERSET is defined when the database is created and specified with the CREATE DATABASE command.
  

• The default value of NLS_NCHAR_CHARACTERSET is AL16UTF16.
  

• From Oracle 9i onwards the NLS_NCHAR_CHARACTERSET can have only 2 values, either UTF8 or AL16UTF16 and both are unicode character sets.
  

• National character set are always defined in CHAR length semantics and you cannot define them in BYTE. That means if you defines NCHAR(5) then 5 maximum characters can be stored regardless of how many bytes they can hold.
  

• Many one thinks that they need to use the NLS_NCHAR_CHARACTERSET to have UNICODE support in oracle but this is not true. One can always use UNICODE in either two ways. Storing data into NCHAR, NVARCHAR2 or NCLOB columns or you can perfectly use "normal" CHAR and VARCHAR2 columns for storing unicode in a database who has a AL32UTF8 / UTF8 NLS_CHARACTERSET.

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