Oracle Default date format modification ____oracle

1. Temporarily modify by using functions, such as:

Select To_char (sysdate, ' Yyyy-mm-dd hh24:mi:ss ') from dual;

2. Modify the date format of the current session:

Alter session set nls_date_format= ' Yyyy-mm-dd HH24:MI:SS ';

3. Permanent modifications,

Adding environment variables-system variables

Key = Nls_date_format  value = YYYY:MM:DD HH24:MI:SS  

The source of the Nls_date_format value in the view v$nls_parameters is not the internal setting of the database, but the environment variables from the operating system