LNNVL is an oracle built in function that returns TRUE for conditions evaluating to FALSE or UNKNOWN, and returns FALSE for conditions evaluating to TRUE. My question is what would be the benefit of returning the opposite of the truth condition rather than just handling the NULL values?
For example, suppose you have an Emp table with StartCommission and CurrentCommission columns which may contain nulls. The following returns only rows with neither value null:
SELECT * FROM Emp WHERE StartCommission = CurrentCommission;
If you wanted to include rows where either commission is null you could do something like this:
SELECT * FROM Emp WHERE StartCommission = CurrentCommission OR StartCommission IS NULL OR CurrentCommission IS NULL;
It would seem like a function would exist to shorten this syntax, but using LNNVL returns all the non-equal records and all the records with nulls.
SELECT * FROM Emp WHERE LNNVL(StartCommission = CurrentCommission);
Adding NOT to this only returns rows without nulls. It seems to me that the desired functionality for this case would be to keep true conditions true, false conditions false, and have unknown conditions evaluate to true. Have I really created a low use case here? Is it really more likely to want to turn unknown into true, true into false, and false into true?
create table emp (StartCommission Number(3,2), CurrentCommission Number(3,2)); insert into emp values (null,null); insert into emp values (null,.1); insert into emp values (.2,null); insert into emp values (.3,.4);