SET SYSTEM VARIABLES - ORACLE/SQL PLUS

SET DEF[INE] {& | c | ON | OFF}

Sets the charavter used to prefix substitution variables to c.

ON or OFF controls whether SQL * Plus will scan commands for substitution variables and replace them with their values.

Example :

sql > SET DEFINE ON

        SELECT 'HELLO & ?' FROM DUAL;

       ? = WORLD   (IT WILL ASK FOR USER INPUT,HERE THE 'WORLD' IS A USER INPUT)

       OUTPUT : "HELLO WORLD"


sql > SET DEFINE OFF
        SELECT 'HELLO & ?' FROM DUAL;

        (IT WON'T ASK FOR USER INPUT AS THE DEFINE IS OFF)

        OUTPUT : "HELLO & ?"