Very interesting subject. If NULL is to be considered as unknown, then SQL should use the 3-valued logic. In that case 
NULL OR TRUE = TRUE
and
NULL AND TRUE = NULL

see also here http://en.wikipedia.org/wiki/Null_(SQL) the section "Comparisons with NULL and the three-valued logic"

It looks like MonetDB is doing the opposite, or could it be that you copy-paste the results in different order? 


On Tue, Sep 2, 2014 at 6:57 PM, Scott Mathieson <scott.mathieson@pb.com> wrote:

Hi,

 

I’ve come across something that is either a bug or is just my misunderstanding of how MonetDB deals with NULL results from boolean expressions.

 

The issue I’m having is the OR and AND expressions behave differently in when evaluating a bollean expression where one of the variable is NULL (This is using  version 11.15.19)

 

If I run a query:

 

SELECT ([some expression that evaluates to NULL] OR [some expression that evaluates to True] ) as “Result” – the returned value is <null>

 

If I try

 

SELECT ([some expression that evaluates to NULL] AND [some expression that evaluates to True] ) as “Result” – the returned value is True

 

This would seem to suggest the AND evaluation is ignoring NULL or Treating NULL as meaning True whereas OR is propagating it. Which is correct and is this a bug?

 

Thanks,

 

Scott Mathieson

 

 

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