How to reference a jsonb coulmn value from a value map in postgres - postgresql

Question

I want to be able to reference the error table for msg and description based on the err_id on the results table for err_map jsonb column, I'd also want to be able relate which error occurred against which column whether the independent columns c1,c2 or val_map jsonb column c3, c4)
the only reason the val_map stores data(with .) as "val_map.c3": 3 so we can identify that these columns were from val_map when mapping errors to columns.
I have a result table
here the err_map column values 1,3 reference to below error table
id | c1 | c2 | val_map | err_map
----------------------------------------------------------------
1 | chk1 | chk2 | {"c3":3, "c4":4} | {"c1": 1, "val_map.c3": 3}
Error Table
id | msg | description
----------------------------------------------------------------
1 | msg1 | an error1 occurred
----------------------------------------------------------------
3 | msg3 | an error3 occurred
I looked at jsonb_each and jsonb_object_keys but can't really figure out how to use it to join these tables. Any help/hints will be appreciated.
Pardon if something is unclear, please ask to provide more detail.
[Edit 1]: removed foreign key reference as it was misleading
[Edit 2]: I've got it working but it's quite inefficient
select
e.error_key,
e.error_message,
T2.key as key
from result.error e
inner join (
select
substring(T1.key, 11) as key,
T1.value
from (
select em.key, em.value
from result rd, jsonb_each(rd.error_map) as em
) as T1
where T1.key like '%value_map%'
union all
select T1.key , T1.value
from (
select em.key, em.value
from result rd, jsonb_each(rd.error_map) as em
) as T1
where T1.key not like '%value_map%'
) as T2 on T2.value::bigint = e.id;

Answer 1

You can simplify that UNION ALL to just
select
e.error_key,
e.error_message,
T2.key as key
from result.error e
inner join (
select
case when T1.key like 'val_map.%'
then substring(T1.key, 9)
else T1.key
end as key,
T1.value
from result rd, jsonb_each(rd.error_map) as T1
) as T2 on T2.value::bigint = e.id;