On Fri, 8 Nov 2002, Ludwig Lim wrote:
> Hi:
>
> I tried the following:
> CREATE TABLE x(
> a NUMERIC(5,0),
> b VARCHAR(5)
> );
>
> CREATE TABLE y(
> a INTEGER,
> b VARCHAR(5)
> );
>
> INSERT INTO x(b) VALUES ('LUDZ');
> INSERT INTO y(b) VALUES ('TEST');
>
> SELECT x.b,y.b FROM x,y WHERE x.a=y.a
> returns zero rows.
A comparison of two NULL values does not
return true, it returns unknown.
If you want to say equal or both null you
should do it explitly.
(x.a=y.a) or (x.a is null and y.a is null)