Postgres 16

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

CREATE FUNCTION f_explain(_qry text, _options text = NULL)
  RETURNS SETOF text
  LANGUAGE plpgsql AS
$func$
BEGIN
  RETURN QUERY EXECUTE
  format('EXPLAIN %s %s', _options, _qry);
END
$func$;

CREATE FUNCTION

SELECT * FROM f_explain('SELECT 1');

f_explain

Result  (cost=0.00..0.01 rows=1 width=4)

SELECT 1

SELECT * FROM f_explain('SELECT 1', '(ANALYZE, BUFFERS)');

f_explain

Result  (cost=0.00..0.01 rows=1 width=4) (actual time=0.001..0.001 rows=1 loops=1)

Planning Time: 0.007 ms

Execution Time: 0.006 ms

SELECT 3