Postgres 13

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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?.

drop table if exists my_table;
create table my_table(
  product char(20) primary key,
  tag1 char(100),
  tag2 char(100) );
  insert into my_table (product,tag1,tag2) values
    ('Product 1', 'AB;AC;AD', 'RXX;ZAC;XAD;AC'), 
    ('Product 2', 'RXX;AC;XAD', 'RP12;X455;R444;AXD');
2 rows affected

select *  from my_table


product
tag1
tag2


Product 1
AB;AC;AD
RXX;ZAC;XAD;AC

Product 2
RXX;AC;XAD
RP12;X455;R444;AXD


SELECT * FROM my_table WHERE  (string_to_array(tag1,';')::text[]) && (string_to_array(tag2,';')::text[])


product
tag1
tag2


Product 1
AB;AC;AD
RXX;ZAC;XAD;AC

product	tag1	tag2
Product 1	AB;AC;AD	RXX;ZAC;XAD;AC
Product 2	RXX;AC;XAD	RP12;X455;R444;AXD