Re: Proper relational database?

On Sat, Apr 23, 2016 at 12:05 AM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> FWIW standard SQL may not allow it but Postgres does, and it's even
> possible to exclude duplicates by using an expression that references
> the whole row.

Indeed, but its semantics can be rather wonky. Witness:

postgres=# select 1;
?column?
----------
1
(1 row)

postgres=# select 1 union select 1;
?column?
----------
1
(1 row)

postgres=# select;
--
(1 row)

postgres=# select union select;
--
(2 rows)

postgres=# select 1 intersect select 1;
?column?
----------
1
(1 row)

postgres=# select intersect select;
--
(2 rows)