Re: Sub-query having NULL row returning FALSE result

Sridhar N Bamandlapally <sridhar.bn1@gmail.com> writes:
> postgres=# CREATE TABLE emp (id INTEGER unique, ename VARCHAR);
> postgres=# INSERT INTO emp VALUES (null, 'aaa');
> ...
> postgres=# INSERT INTO emp SELECT * FROM (SELECT 5::integer id,
> 'eee'::varchar ename) nr WHERE id NOT IN (SELECT id FROM emp);
> INSERT 0 0

This is expected.  NOT IN can never succeed if there are any nulls
returned by the sub-select, because the nulls represent "unknown",
and so it's unknown whether there is a match to the outer "id"
value, and WHERE takes a null (unknown) result as false not true.
Certainly there are things to quibble with in that behavior, but
it's what's been required by the SQL standard since 1992.

> but this is working with other databases

Really?  None that are compliant with the SQL standard, for sure.

            regards, tom lane