What is the difference between the views nls_database_parameters and nls_instance_parameters?

The NLS_DATABASE_PARAMETERS view will display what the NLS settings were when the database was created. These are fixed at the database level and cannot be changed.

The NLS_INSTANCE_PARAMETERS view reflects parameters set for your instance in the init.ora file or the server parameter file (spfile).


Source: James Koopman in Databasejournal.com

This matches my settings for a random database:

SQL> show parameter nls_
 
NAME                                  TYPE        VALUE
 ------------------------------------ ----------- ------------------------------
 nls_comp                             string      BINARY
 nls_language                         string      AMERICAN
 nls_length_semantics                 string      BYTE
 nls_nchar_conv_excp                  string      FALSE
 nls_territory                        string      AMERICA
 
SQL> SELECT * FROM NLS_INSTANCE_PARAMETERS WHERE value IS NOT NULL;
 
PARAMETER                       VALUE
 ------------------------------ ----------------------------------------
 NLS_LANGUAGE                   AMERICAN
 NLS_TERRITORY                  AMERICA
 NLS_COMP                       BINARY
 NLS_LENGTH_SEMANTICS           BYTE
 NLS_NCHAR_CONV_EXCP            FALSE
 
5 rows selected.