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 table plan (
  plan_no varchar(20), 
  weight integer
  );

CREATE TABLE


insert into plan values 
('T190234', 21),
('T190234', 14),
('T190234', 35),
('T190245', 100),
('T190245', 80),
('T190339', 12),
('T190339', 45),
('T190339', 33);

INSERT 0 8


select 
 plan_no, 
 weight, 
 sum(weight) over (partition by plan_no) as total_weight
from plan


plan_no
weight
total_weight


T190234
21
70

T190234
14
70

T190234
35
70

T190245
100
180

T190245
80
180

T190339
12
90

T190339
45
90

T190339
33
90



SELECT 8

plan_no	weight	total_weight
T190234	21	70
T190234	14	70
T190234	35	70
T190245	100	180
T190245	80	180
T190339	12	90
T190339	45	90
T190339	33	90