[Mondrian] NULL literal

[Richard Emberson]

I've never seen the MDX specification - I think that
whatever MS does is the spec. Anyway,
Mosha Pasumansky is the author(??) of MDX and
from a couple of his web pages I find:

"First, it notices, that for A*B will be NULL
if either A or B is NULL."
- half way down the page
http://www.mosha.com/msolap/articles/multiplication_perf.htm


"and NULL/NULL is defined as NULL in MDX."
1/8 of the way down the page
http://www.feedshow.com/show_items-feed=fdef23d0a3fde71fe9631652cff7ea79

So I assume that for expressions like a+b,a-b,a*b,a/b if either
a or b are NULL then:
NULL+b == b
a + NULL == a
NULL - b == -b
a - NULL == a
a*NULL == NULL
NULL*b == NULL
a/NULL == NULL
NULL/b == NULL
and if both are NULL then the result is NULL.

The NULL Literal when compiled become an ConstantCalc
instance.
The change I believe is needed is in the ConstantCalc
constructor. If the constructor parameter 'o' which
is of type Object is a Java null, then the instance
variables have the values:

Object o = null;
int i = FunUtil.IntegerNull
double d = FunUtil.DoubleNull

Richard


FYI

For Empty I've found this page:
http://msdn2.microsoft.com/en-us/library/aa216761(SQL.80).aspx

specifically:
"When the empty cell value is an operand for any of the numeric 
operators (+, -, *, /), it behaves like the number zero."

michael bienstein wrote:
> My understanding is as follows:
> NULL as a value (not literal) is for Members that do not exist 
> physically but do logically such as [Geography].[All Geography].Parent.  
> When you pull a cell value for which one member of the context is NULL, 
> you get a NULL value as a numeric (or String etc) for the cell value as 
> opposed to an EMPTY value which is when the membes all exist but there 
> is no value in the cube at that position.
> 
> After that there's lots of tricky things you can do with numeric NULL 
> values like addition, multiplication etc E.g. A is a numeric expression 
> that evaluates to NULL and B is a numeric expression that doesn't.  What 
> does A+B evaluate to?
> 
> As for the 'IS NULL' construct, that's to test Member expression and 
> numeric expression for having the NULL value given that NULL=NULL yields 
> false.  You can also use NULL explicitly in Range function:
> [Time].[1997].FirstChild : NULL
> 
> Here's an example of an MDX query that should test a problem (not tested 
> anywhere):
> 
> WITH MEMBER [Time].[1997].[Test] AS '[Time].[1997]+0'
> SELECT
> {[Time].[1997], [Time].[1997].[Test]} on COLUMNS,
> {[Store].[All Stores].Parent} on ROWS
> FROM [Warehouse Sales]
> 
> Michael
> 
> PS: I've got code for running multiple tasks going but without test 
> cases.  Found some time.  Taking longer than expected.  Will post by 
> next week but don't want to disturb your efforts to release.
> 
> 
> 
> 
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