I have rows as shown below
ProductId ProductName ProductDesc ProductLoc
101 Camel Pencil B-10
102 Parker Pen
103 Mirado Pen C-10
WHERE productloc = NVL ('', productloc)
select * from tablename;
Is what you need in that case because your where gives no effect. You compare column with itself.
If you want to filter and include nulls you can do (but probably replace one
productloc with some value:
select * from tablename where productloc = productloc or productloc is null;
select * from tablename where nvl(productloc, 'SOME_UNIQUE_VAL') = nvl(productloc, 'SOME_UNIQUE_VAL');
and also replace one of
productloc by some value.