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

The following bug has been logged on the website:

Bug reference:      16862
Logged by:          Дмитрий Иванов
Email address:      firstdismay@gmail.com
PostgreSQL version: 12.5
Operating system:   Windows 10
Description:

Good day!
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

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

=?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