On Mon, 22 Apr 2002 pgsql-bugs@postgresql.org wrote:
> Florian Steffen (mailing-list@urbanet.ch) reports a bug with a severity of 3
> The lower the number the more severe it is.
>
> Short Description
> Buggy select statment with numeric
>
> Long Description
> A select statement with a where clause on a numeric column tested
> for equality against null always return empty result. With ISNULL
> everything is fine, but not with the = operator.
This is correct behavior. NULL=NULL is unknown not true. Older versions
had a hack to make an explicit =NULL the same as IS NULL for certain
clients that emitted such statements when they meant IS NULL. This is now
off by default but can be turned on using the set variable
TRANSFORM_NULL_EQUALS.