On Mon, May 21, 2018 at 5:54 AM, Alexey Dokuchaev <danfe@nsu.ru> wrote:
result := json_agg(_) FROM ( SELECT foo, bar, baz ... FROM t1, t2, t3 WHERE ...) AS _; -- this works fine
GET DIAGNOSTICS retcode = ROW_COUNT; -- always returns 1
I'd expected `retcode' to contain the number of SELECT'ed rows, but it is something else (always 1). Apparently, aggregation functions like json_agg()/array_agg() mangle the ROW_COUNT from the inner SELECT (the one I'm interested in).
Is this expected and correct behavior?
Yes, the query returned only one row, with a single json column. You wrote the equivalent of:
SELECT json_agg(...) FROM ... INTO result;
And you are getting the count of the top-most select (which is implied in the syntax that you used).
Is it possible to obtain the first ROW_COUNT (after SELECT) without performing it twice?
Not directly, no. You should execute the inner query to a temporary table than perform your counting and json_agg from that.
