Re: Max date

On Wed, Sep 23, 2015 at 2:13 PM, John Yeung <gallium.arsenide@xxxxxxxxx>
wrote:

Let's say I have a nullable variable call MYVAR. And let's say that
its null indicator is currently on. So in SQL, MYVAR is simply equal
to NULL. But in RPG, I can do this:

myvar = 5; // null indicator is not affected
x = %nullind(myvar); // x = '1'
y = (myvar > 2); // y = '1'

In SQL, MYVAR > 2 would be False, since any comparison with NULL is
False.

​No, no it wouldn't and no, no it isn't...

In SQL,
when MYVAR is NULL
​ then ​
MYVAR > 2 is unknown; neither true or false.

​If as you say MYVAR > 2 was FALSE, then NOT (MYVAR > 2) would be true and
it's not.

I'm sure you realize this, but it just goes to show how easy it is to screw
up 3 valued logic.

Going back to the OP, if expiration date is nullable with NULL standing in
for NO EXPIRATION, then​ the only way to return a list of non-expired
records would be to
select *
from myfile
where myexp is null or myexp > CURRENT_DATE

You can pull a list of expired records with a simple
select *
from myfile
where myexp <= CURRENT_DATE

And boolean logic would tell you that this should give non-expired
records...
select *
from myfile
where NOT (myexp <= CURRENT_DATE)

But it won't when myexp contains a NULL value.