To show parameter in detail
SQL> SHOW DEFINE;
To escape from substitution variable (&):
SQL> SET DEFINE OFF;
To enable DBMS_OUTPUT:
SQL> SET SERVEROUTPUT ON;
To see old and new values of variables:
SQL> SET VERIFY ON;
To calculate total execution time of SQL:
SQL> SET TIMING ON;
To print time on the SQL terminal:
SQL> SET TIME ON;
To see table columns name and types for a table:
SQL> DESC hr.employees@XE;
To see currently logged-in user:
SQL> SHOW user;