nullability for join stage

[cetzhbo]

Hello Gurus,

following is the fact for join stage:

when we use Join stage, Be particularly careful to observe the nullability properties for input links to any form of Outer Join. Even if the source data is not nullable, the non-key columns must be defined as nullable in the Join stage input in order to identify unmatched records.

why does this rule exist for join stage ?

thanks very much!

[ray.wurlod]

Because, by definition, any Outer Join returns NULL in all columns defined on its unmatched input.

This is regular SQL, not just DataStage.