Postgres 15

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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?.

select now(),version(),setseed(.42);


now
version
setseed


2024-05-01 20:37:00.744756+01
PostgreSQL 15.0 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10), 64-bit




SELECT 1


--I have a table my_table like this:
create table my_table(id,updated_at,status) as values
  ('ID1','2023-12-18 18:37:21.724825+00'::timestamptz, 'I')
 ,('ID1','2024-01-02 23:08:03.50741+00 ', 'I')
 ,('ID1','2024-01-03 23:07:03.892617+00', 'I')
 ,('ID1','2024-01-06 23:09:00.877018+00', 'A')
 ,('ID1','2024-01-07 23:08:03.134111+00', 'A')
 ,('ID1','2024-01-08 23:06:31.164932+00', 'A')
 ,('ID1','2024-03-03 23:39:39.138697+00', 'A')
 ,('ID1','2024-03-04 23:55:54.582789+00', 'F')
 ,('ID1','2024-03-05 23:37:15.70314+00 ', 'F')
 ,('ID1','2024-03-06 23:47:16.814729+00', 'F')
 ,('ID1','2024-03-07 23:42:54.349137+00', 'A')
 ,('ID1','2024-03-08 23:35:53.188792+00', 'A')
 ,('ID1','2024-03-09 23:30:55.979575+00', 'A')
 ,('ID1','2024-04-10 08:30:05.329453+00', 'F')
 ,('ID2','2024-03-15 23:52:28.005298+00', 'A')
 ,('ID2','2024-03-16 23:53:38.031816+00', 'A')
 ,('ID2','2024-03-17 23:57:42.556396+00', 'A')
 ,('ID2','2024-03-18 13:33:38.264444+00', 'A')
 ,('ID2','2024-03-18 22:48:29.366489+00', 'A')
 ,('ID2','2024-03-19 15:00:02.19655+00 ', 'F')
 ,('ID2','2024-03-26 18:37:13.514644+00', 'A')
 ,('ID2','2024-03-27 15:19:13.823159+00', 'F')
 ,('ID2','2024-03-28 15:31:46.841049+00', 'F')
 ,('ID2','2024-04-03 07:43:08.253604+00', 'P')
;
--I would like to select from it the dates at which the status changes 
--from any value to the value F, i.e I am expecting the following output:
/*
ID1   | 2024-03-04 23:55:54.582789+00
ID1   | 2024-04-10 08:30:05.329453+00
ID2   | 2024-03-19 15:00:02.19655+00
ID2   | 2024-03-27 15:19:13.823159+00
*/
--So far, I managed to get the first time such a change 
--occurs for each id, but I can't get subsequent changes. Here is my query:

    SELECT
        id, updated_at
    FROM (
        SELECT
            *
            , RANK() OVER (PARTITION BY id ORDER BY updated_at ASC) AS rank_
        FROM ( SELECT * FROM my_table WHERE status='F' ) t_sub
    ) T
    WHERE rank_ = 1
--How to change it to get not only the first time each id turns to the status F, 
--but also second, third, fourth, etc... changes to F?

SELECT 24




id
updated_at


ID1
2024-03-04 23:55:54.582789+00

ID2
2024-03-19 15:00:02.19655+00



SELECT 2


select id,updated_at 
from(select *
           ,status<>lag(status,1,status)over w1 and status='F' as changed_to_f
     from my_table
     window w1 as (partition by id order by updated_at) ) as subquery
where changed_to_f
order by 1,2;


id
updated_at


ID1
2024-03-04 23:55:54.582789+00

ID1
2024-04-10 09:30:05.329453+01

ID2
2024-03-19 15:00:02.19655+00

ID2
2024-03-27 15:19:13.823159+00



SELECT 4

id	updated_at
ID1	2024-03-04 23:55:54.582789+00
ID2	2024-03-19 15:00:02.19655+00

id	updated_at
ID1	2024-03-04 23:55:54.582789+00
ID1	2024-04-10 09:30:05.329453+01
ID2	2024-03-19 15:00:02.19655+00
ID2	2024-03-27 15:19:13.823159+00