NVL2 returns one value when the value of a specified expression is not null, or another value when the value of the specified expression is null.
To replace a null value with a string, use NVL.
Data type of the first argument
NVL2(expr1, expr2, expr3)
expr1 is the base expression whose value this function evaluates.
expr2 is an expression whose value is returned when expr1 is not null.
expr3 is an expression whose value is returned when expr1 is null.
NVL2('Which string?', 'First String', 'Second String') returns the value First String.