BUG #16862: Unexpected result of checking for null "IS NOT NULL" in function

PG Bug reporting form <noreply@postgresql.org> writes:

1. Create TABLE: "bpd"."group" AND view
2. Create FUNCTION:
DECLARE: egroupV "bpd"."vgroup"%ROWTYPE; view
DECLARE: egroupT "bpd"."group"%ROWTYPE; table
3. Retrieving data checking the result in function:
SELECT * INTO egroupV FROM "bpd"."vgroup" WHERE id = iid;
SELECT * INTO egroupT FROM "bpd"."group" WHERE id = iid;
IF (egroupV IS NOT NULL) THEN => state OK
IF (egroupT IS NOT NULL) THEN => state OK
IF NOT(egroupV IS NULL) THEN => state OK
IF NOT(egroupT IS NULL) THEN => state OK
4. ALTER TABLE "bpd"."group" ADD COLUMN
5. Retrieving data checking the result in function:
SELECT * INTO egroup FROM "bpd"."vgroup" WHERE id = iid;
SELECT * INTO egroupT FROM "bpd"."group" WHERE id = iid;
IF (egroupV IS NOT NULL) THEN => state OK
IF (egroupT IS NOT NULL) THEN => state NOT WORK???????????
IF NOT(egroupV IS NULL) THEN => state OK
IF NOT(egroupT IS NULL) THEN => state OK

It's impossible to make any sense of this report. What do you
think "not work" means? You have not provided enough detail to
let someone else reproduce whatever you're seeing, either.

Please read
https://wiki.postgresql.org/wiki/Guide_to_reporting_problems

regards, tom lane

=?UTF-8?B?0JTQvNC40YLRgNC40Lkg0JjQstCw0L3QvtCy?= <firstdismay@gmail.com> writes:

Does not work means does not produce the expected result. It seemed
obvious to me.

If it were obvious I wouldn't be asking you for more information.
You've left out a lot, like the table details and any sample data
that might be necessary to reproduce the problem.

The link I sent you offers some suggestions about how to create
a self-contained problem report. Ideally, provide a SQL script
that anyone can run in an empty database to see the misbehavior.

Also, please keep the mailing list cc'd. I'm not the only
developer who might take an interest in this problem, once
we understand what it is.

regards, tom lane

On Fri, Feb 12, 2021 at 3:05 AM PG Bug reporting form <
noreply@postgresql.org> wrote:

1. Create TABLE: "bpd"."group" AND view
4. ALTER TABLE "bpd"."group" ADD COLUMN

IF (egroupV IS NOT NULL) THEN => state OK
IF (egroupT IS NOT NULL) THEN => state NOT WORK???????????

I agree with Tom that this report needs more commentary, not just code and
"ok/not work". But I believe there are two behaviors in PostgreSQL that
you are unaware of that lead to your confusion.

First:
"If the expression is row-valued, then IS NULL is true when the row
expression itself is null or when all the row's fields are null, while IS
NOT NULL is true when the row expression itself is non-null and all the
row's fields are non-null. Because of this behavior, IS NULL and IS NOT
NULL do not always return inverse results for row-valued expressions;"

https://www.postgresql.org/docs/current/functions-comparison.html

Second:
While you've altered the table bpd.group, adding a column, you didn't do
the same to the view and so that view does not include that column.

Those two things combined, specifically the newly added column being left
null causing the is not null check to return false, likely explain why the
behavior you observe is not a bug.

David J.

=?UTF-8?B?0JTQvNC40YLRgNC40Lkg0JjQstCw0L3QvtCy?= <firstdismay@gmail.com> writes:

CREATE TABLE "public"."test" (
"id" Bigint NOT NULL,
"name" Character Varying NOT NULL,
PRIMARY KEY ( "id" ) );
-- -------------------------------------------------------------
INSERT INTO "public"."test" ( "id", "name")
VALUES ( 1, 'sdsdsdsdsd' );
CREATE OR REPLACE VIEW "public"."vtest" AS SELECT test.id,
test.name
FROM test;;

-- CREATE FUNCTION "class_is_actual3( int8, timestamp, timestamp )"
CREATE OR REPLACE FUNCTION test_is_null_id(iid bigint, OUT tr BOOLEAN, OUT
vr BOOLEAN)
RETURNS RECORD
LANGUAGE plpgsql
AS $function$
DECLARE
t "test"%ROWTYPE;
v "vtest"%ROWTYPE;

BEGIN
SELECT * INTO t FROM ONLY test WHERE id = iid;
SELECT * INTO v FROM ONLY vtest WHERE id = iid;

IF t IS NOT NULL THEN
tr = true;
ELSE
tr = false;
END IF;

IF v IS NOT NULL THEN
vr = true;
ELSE
vr = false;
END IF;
END;
$function$;
-- -------------------------------------------------------------
SELECT * FROM test_is_null_id(1);

ALTER TABLE "public"."test" ADD COLUMN "New_olumn" Bigint[] NULL;

SELECT * FROM test_is_null_id(1);

OK, I appreciate the test case, but as far as I can see the database
is doing exactly what it's supposed to. After the ALTER ADD COLUMN
we have

# table test;
id | name | New_olumn
----+------------+-----------
1 | sdsdsdsdsd |
(1 row)

# table vtest;
id | name
----+------------
1 | sdsdsdsdsd
(1 row)

# SELECT * FROM test_is_null_id(1);
tr | vr
----+----
f | t
(1 row)

That looks fine to me: "test" now contains a column that is null,
so it doesn't pass the IS NOT NULL test. On the other hand,
"vtest" doesn't contain that column; all its columns are still non
null, so it does pass the IS NOT NULL test.

Note that "foo IS NOT NULL" is not the same as "NOT (foo IS NULL)"
when foo is of composite type. I agree that's confusing, but it's
required by the SQL spec. See
https://www.postgresql.org/docs/12/functions-comparison.html

regards, tom lane