To evaluate a specified expression and replace a non-
NA value or empty string with one value and a
NA value with another, use NVL2.
The specified replacement value when the value of the base expression is
NA, or the base expression when the value of the base expression is not
NA. The data type of the return value is always the same as the data type of the base expression.
NVL (exp , replacement-exp)
The expression that you want to replace when it has a
NA value or an empty string.
The value with which you want to replace a