Postgres 14

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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?.

begin;
create temp table a2(col1 text, col2 text, col3 text);
insert into a2(col1,col2,col3) values
('a','abc' , 'rejected'),
('a', 'def',null    ),
('b' , 'etg'  ,  'accepted'),
('c', 'jfh',null);
commit;


table a2;




4 rows affected



col1
col2
col3


a
abc
rejected

a
def
null

b
etg
accepted

c
jfh
null


update a2 set
                col3 =
                  case when col1 = 'a' then 'rejected'
                  when col1 = 'b' then 'accepted'
                  when col1 = 'c' then 'null' end
where col3 is  null
returning *;


col1
col2
col3


a
def
rejected

c
jfh
null


drop table a2 cascade ;