On 9/18/22 13:25, Bryn Llewellyn wrote:
> I noticed that "array()" is used in the query that implements the "\du"
> psql meta-command. It has some similarity with "array_agg()" thus:
>
> create temporary view x(v) as (values (17), (42));
> select array_agg(v) from x;
> select array(select v from x);
>
> But there are differences. The "array()" function requires that its
> argument is a subquery that returns a single column. (Its data type can
> be composite.) But the "array_agg()" function's argument must be the
> select list in the larger context of a select statement—and in general
> together with "group by".
>
Lack of an explicit GROUP BY falls through to an implied one:
https://www.postgresql.org/docs/current/sql-select.html#SQL-GROUPBY
"If there are aggregate functions but no GROUP BY clause, the query is
treated as having a single group comprising all the selected rows."
--
Adrian Klaver
adrian.klaver@aklaver.com
