Not able to figure out the exact PostgreSQL query - sql

Question

I have a set of postgreSQL data which looks like the one in the attached pic(Pic1-Sample Data) :
custom_field column would identify if the row entry is 'Department ID' or 'High Priority Role?' and the first six digits of text_value column would give the department codes.
As you can see value in the text_value column is 'Yes' wherever the custom_field is 'High Priority Role?'
Now my requirement is to extract only those records where custom_field is 'High Priority Role'. This sounds very simple but it should also have the 'Department ID' attached to it.
NOTE: job_id is not unique. Each job_id corresponding to 'High Priority Role?' would also have a duplicate entry for which the value in custom_field would be 'Department ID'(see attached Pic 2 for reference).

Answer 1

Something like this?
select
a.*,
b.display_value as department
from (
select
*
from
<table>
where
custom_field = 'High Priority Role?'
) a
inner join
<table> b
on
a.job_id = b.job_id
where
b.custom_field != 'High Priority Role?'
group by
a.job_id,
a.custom_field,
a.float_value,
a.date_value,
a.display_value,
a.text_value,
a.unit,
b.display_value
I've tested in MariaDB, not PostgreSQL, but it should work.
http://sqlfiddle.com/#!15/62ca4/3/0

Answer 2

This is a simple join:
select t.*, left(t2.text_value, 6) as department_id
from t join
t t2
on t.job_id = t2.job_id and
t.custom_field = 'High Priority Role?' and
t2.custom_field <> 'High Priority Role?';
This assumes that there is exactly one matching job with the department id.
If there are multiple, then go for a lateral join:
select t.*, left(t2.text_value, 6) as department_id
from t, lateral
(select t2.*
from t t2
where t.job_id = t2.job_id and
t.custom_field = 'High Priority Role?' and
t2.custom_field <> 'High Priority Role?'
fetch first 1 row only -- no `order by` because any match will do
) t2;