> There it is again. What does length(NULL) mean ? Should it be NULL because
> anything derived from "Don't know" is "Don't know" ? Or should it be a non-
> negative integer representing how long the NULL value is ? I may have missed
> it, but I don't think the answer is in SQL92. The only solution is not to
> depend on any particular behaviour.
The result of any operation involving NULL other than IS NULL and IS NOT NULL
must be NULL.
Note that the coalese(x,y) is just
CASE WHEN x IS NULL THEN y ELSE x END
and coalesce(x,y,z) is
CASE WHEN x IS NULL THEN CASE WHEN y IS NULL THEN z ELSE y END ELSE x
END
and so forth.
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