Thread: Trouble in SELECT query

I have a PostgreSQL 7.1. When I start query like "SELECT * FROM table1 WHER=
E field1 =3D NULL;" it working OK, but query like "SELECT * FROM table1 WHE=
RE field1 <> NULL" returns the void result. Field "field1" has type DATE. "=
... field1 IS NULL", "... field1 IS NOT NULL", "... field1 <> 0" also worki=
ng correctly. "... field1 =3D 0" also not working.

        With best regards, Serg Matskov.

Serg Matskov writes:

> I have a PostgreSQL 7.1. When I start query like "SELECT * FROM table1
> WHERE field1 = NULL;" it working OK, but query like "SELECT * FROM
> table1 WHERE field1 <> NULL" returns the void result. Field "field1"
> has type DATE. "... field1 IS NULL", "... field1 IS NOT NULL", "...
> field1 <> 0" also working correctly. "... field1 = 0" also not
> working.

'field <> NULL' is always false, so it's not surprising that no rows are
returned.  'field = NULL' should also be false, but PostgreSQL treats it
as 'field IS NULL' to allow broken clients to work.  See also
<http://www.de.postgresql.org/users-lounge/docs/7.1/postgres/functions-comparison.html>.

--
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter