PL/SQL Character Set

A PL/SQL program is a sequence of statements, contains multiple lines of text. The types of characters available depend on the database character set you’re using. To know your current Oracle Database character set, run the following SQL statement:

Get PL/SQL Character Set

Select value character_set From nls_database_parameters
  Where parameter='NLS_CHARACTERSET';

Suppose if you are using the US7ASCII character set for your Oracle Database, the following characters will be available to you:

Character List of PL/SQL US7ASCII Character Set

Letters: A–Z, a–z
Digits: 0–9
Symbols: ~ ! @ # $ % * () _ − + = | : ; “ ‘ < > , . ? / ^
Whitespace: Tab, space, newline, carriage return

Changing the Oracle Database Character Set

To change the Oracle Database character set, use the following sequence of commands. But please take a backup of the full Oracle Database before changing the character set because it can not be rolled back.

STARTUP MOUNT;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
ALTER SYSTEM SET AQ_TM_PROCESSES=0;
ALTER DATABASE OPEN;
ALTER DATABASE CHARACTER SET new_character_set;
SHUTDOWN IMMEDIATE; -- or SHUTDOWN NORMAL; 
STARTUP;

You can check the following Oracle Docs on Character set: