On 12/9/25 18:29, David G. Johnston wrote:
> On Tue, Dec 9, 2025 at 10:14 AM Thiemo Kellner
> <thiemo@gelassene-pferde.biz> wrote:
>
> I feel, you meant to say, the subquery does not return any record
> which is not the same as returns NULL.
>
>
> For a scalar subquery the final output of a zero-row query is the null
> value.
>
To me, it does not look like that (please note the empty line in the
last example). Can you point me to the documentation saying that 0 rows
is sometimes equal to 1 row?
postgres=# select * from pg_user;
usename | usesysid | usecreatedb | usesuper | userepl | usebypassrls
| passwd | valuntil | useconfig
----------+----------+-------------+----------+---------+--------------+----------+----------+-----------
postgres | 10 | t | t | t | t |
******** | |
(1 row)
postgres=# select usename from pg_user where false;
usename
---------
(0 rows)
postgres=# select null as usename from pg_user;
usename
---------
(1 row)
