comparing with null values

dnat · Post by **dnat** » Wed Apr 08, 2009 3:42 am

Hi,

When we compare two fields

If (link1.A=Link1.B) then 1 Else 0

Now when Link1.B is a null value what would be the result?

miwinter · Post by **miwinter** » Wed Apr 08, 2009 4:18 am

The row is a reject

dnat · Post by **dnat** » Wed Apr 08, 2009 4:50 am

what would be the value..1 or 0?

basu.ds · Post by **basu.ds** » Wed Apr 08, 2009 5:34 am

reject means '0'

ray.wurlod · Post by **ray.wurlod** » Wed Apr 08, 2009 7:22 am

If link.B is null then (link.A = link.B) is null.
The rule in server jobs (in DataStage BASIC) is that, if the test expression is null, then the Else path is taken, on the grounds that one can not assert that null is "true". The Else path is taken if the expression is not true (which is not necessarily the same thing as "false").
Welcome to the world of no data types, where rules of this kind are necessary.

chulett · Post by **chulett** » Wed Apr 08, 2009 7:55 am

And welcome to E.F. Codd's world of three-valued logic: True, False and Who the Heck Knows.