SQL

oracle nvl

-- force output for NOT NULL values
NVL(your_variable, Value_if_null)

-- OR (force outputs for both NOT NULL and NULL values)
NVL2(your_variable, value_if_not_null, value_if_null)

nvl in oracle

SELECT NVL(NULL, 'N/A') FROM dual;

oracle nvl2

NVL2( string_to_test, value_if_NOT_null, value_if_null )

difference between nvl and nvl2 in oracle

/*
NVL checks if first argument is null and returns second argument.

NVL2 has different logic. If first argument is not null 
then NVL2 returns second argument, but in other case it will 
return third argument.
*/

select nvl(null, 'arg2') from dual
-- Result: arg2;
select nvl2('arg1', 'arg2', 'arg3') from dual 
-- Result: arg2
select nvl2(null, 'arg2', 'arg3') from dual
-- Result: arg3