Postgres 11

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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 table tbl (id int, startDate timestamp, endDate timestamp, plan_id int, planned bool, machine int);
insert into tbl values
  (2005,  '2019-01-16 08:29:24.872736',    '2019-01-16 08:30:23.529706',        34,          true,              6),
  (2004,  '2019-01-16 08:19:28.011148',    '2019-01-16 08:29:22.680828',        34,          true,              6),    
  (2003,  '2019-01-16 08:18:27.074312',    '2019-01-16 08:19:25.753475',        34,          true,              6),
  (2002,  '2019-01-16 08:08:30.206288',    '2019-01-16 08:18:24.856308',        34,          true,              6),
  (2001,  '2019-01-16 08:07:29.163124',    '2019-01-16 08:08:27.949013',        34,          true,              6),
  (2000,  '2019-01-16 07:59:03.221309',    '2019-01-16 08:00:14.654391',        null,        false,             7),
  (1999,  '2019-01-16 08:00:00.986367',    '2019-01-16 08:00:03.221309',        null,        false,             6),
  (1998,  '2019-01-16 07:57:30.711044',    '2019-01-16 07:59:58.778444',        null,        false,             6),
  (1997,  '2019-01-16 07:56:32.466508',    '2019-01-16 07:57:28.489287',        null,        false,             6),
  (1996,  '2019-01-16 07:50:06.887349',    '2019-01-16 07:56:30.237725',        null,        false,             6),
  (1995,  '2019-01-16 07:46:34.327582',    '2019-01-16 07:50:04.619592',        33,          true,              6),
  (1994,  '2019-01-16 07:45:33.813483',    '2019-01-16 07:46:32.014849',        33,          true,              6),
  (1993,  '2019-01-16 07:24:39.267365',    '2019-01-16 07:39:23.786911',        null,        false,             6),
  (1992,  '2019-01-16 07:23:39.646218',    '2019-01-16 07:24:37.093414',        null,        false,             6),
  (1991,  '2019-01-16 07:13:41.166337',    '2019-01-16 07:23:37.403375',        null,        false,             6),
  (1990,  '2019-01-16 07:12:39.961234',    '2019-01-16 07:13:38.907838',        null,        false,             6),
  (1989,  '2019-01-16 07:10:46.984236',    '2019-01-16 07:12:37.647108',        null,        false,             6),
  (1988,  '2019-01-15 17:05:59.832834',    '2019-01-15 17:08:21.603931',        31,          true,              6),
  (1987,  '2019-01-15 17:04:59.567046',    '2019-01-15 17:05:57.565188',        31,          true,              6),
  (1986,  '2019-01-15 17:00:01.411266',    '2019-01-15 17:10:57.255158',        31,          true,              7);

20 rows affected

blockstartdate	blockenddate	ids
2019-01-16 07:10:46.984236	2019-01-16 07:39:23.786911	{1989,1990,1991,1992,1993}
2019-01-16 07:50:06.887349	2019-01-16 08:00:03.221309	{1996,1997,1998,1999}