GROUP BY using tablename.* does not work if tablename has 1 column with NULL values

Hi,

In the below example, t1 points to a table with just 1 column (lastName) and so I expect the 2 SELECT queries (pasted below) using t1.lastName or t1.* syntax to produce the exact same results. But the latter produces one extra row of output (3 rows vs 2 rows).

$ psql --version

psql (PostgreSQL) 13.4 (Ubuntu 13.4-0ubuntu0.21.04.1)

$ psql db

db=> DROP TABLE IF EXISTS tmp;

DROP TABLE

db=> CREATE TABLE tmp (id INTEGER PRIMARY KEY, firstName VARCHAR(30), lastName VARCHAR(30));

CREATE TABLE

db=> INSERT INTO tmp VALUES (1,'Acid','Burn');

INSERT 0 1

db=> INSERT INTO tmp VALUES (2,'Joey',NULL);

INSERT 0 1

db=> SELECT COUNT(t1.lastName) FROM tmp t2 LEFT JOIN (SELECT lastName FROM tmp) AS t1 ON (t2.firstName <= 'Acid') GROUP BY t1.lastName;

count

0

1

(2 rows)

db=> SELECT COUNT(t1.*) FROM tmp t2 LEFT JOIN (SELECT lastName FROM tmp) AS t1 ON (t2.firstName <= 'Acid') GROUP BY t1.*;

count

1

1

0

(3 rows)

It seems like a Postgres bug to me. Not sure if there is a Postgres setting that I need to enable in order to avoid this discrepancy.

Let me know if you need any more information.

Thanks,

Narayanan.