andrew@tao11.riddles.org.uk writes:
> select (select array_agg(random()*i) from (values (1),(2)) v(a)) from
> generate_series(1,3) i;
> Expected output is three rows each with a 2-element array; actual output
> is:
> ERROR: more than one row returned by a subquery used as an expression
> Looking at the explain, the aggregate is being pulled out of the subplan and
> evaluated at the top query level. (This came up while doing some random data
> generation, I've simplified it a bit.)
This is not a bug, it's the behavior required by SQL standard. An
aggregate belongs to the lowest query level supplying a variable to it
(except of course when it contains no variable at all). So it's
effectively an outer-reference constant for that inner select.
regards, tom lane
