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?.

select version();

version

PostgreSQL 11.8 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5), 64-bit

select regexp_split_to_table('NED,SED,ZED,MED',',');

regexp_split_to_table

NED

SED

ZED

MED

select unnest(string_to_array('NED,SED,ZED,MED',','));

unnest

NED

SED

ZED

MED

select row_number() over() type_id,type_val 
  from (select unnest(string_to_array('NED,SED,ZED,MED',',')) type_val ) sl 

type_id
type_val

1
NED

2
SED

3
ZED

4
MED

create table details
           (
             title varchar 
           , misc varchar
           );
insert into details(title, misc )
     values ('DBA','5 years');
1 rows affected

with split_list(type_id,type_val) as
     ( select row_number() over() type_id,type_val 
         from (select unnest(string_to_array('NED,SED,ZED,MED',',')) type_val ) sl 
     )         
select title, type_id, type_val
  from details
 cross join split_list
 where type_id != 4;  

title
type_id
type_val

DBA
1
NED

DBA
2
SED

DBA
3
ZED