Postgresql Use a specified value instead of first_value - postgresql

Question

I am trying to replace first_value and use a specified value to use in an equation because of alpha sort I'm having an issue. I want to use a value in a row called 'control' which is in the segment column and direct_mail_test table. So I need to find a way to call just that value ('control') to then use in the equation. New to PostgreSQL, any help would be greatly appreciated.
Here is my current code
select segment,
count(*) as total,
count(b.c_guid) as bookings,
100.0 * count(b.c_guid)/count(*) as percent,
100.0 * count(b.c_guid) / first_value(count(b.c_guid)) over ( order by segment asc ) as comp
from mailing_tests
left join (
select distinct g.contact_guid as c_guid
from guest g
inner join booking
on booking.guid = g.booking_guid
where booking.book_date >= {{date_start}}
[[and booking.book_date < {{date_end}}]]
and booking.status in ('Booked')
) b
on mailing_tests.guid = b.c_guid
where {{project}}
group by segment
order by segment asc
Here is my output:
segment
total bookings percent comp
catalog 4,091 30 0.73 100
control 30,611 359 1.17 1,196.67
direct_mail 30,611 393 1.28 1,310
online_ads 30,611 371 1.21 1,236.67
'''
As of now its taking in the 'catalog' as the
measurable and I need it to take the 'control' as the
measurable.
Just to put some more context on the code, I am using
metabase. So the {{date_start}}
[[and peak15_booking.book_date < {{date_end}}]]
{{project}}
are all variable functions used in metabase.
I tried to use the nth_value, fetch function, and
many others, but I'm not sure if I am even using
those properly. I have been unsuccessful in finding
any answer to this.

Answer 1

I found a way to make this work, but not sure if it's the cleanest way to do this or if I will run into future issues. I still haven't figured out how to replace first_value, but I did add (order by segment='control' desc) twice. once in the SELECT statement and the other in WHERE clause. Again, not sure if this is the correct way to do this, but thought I would show that I did end up figuring it out. Not sure if I should of answered my own question or deleted it, but thought that this might help someone else.
'
select segment,
count(*) as total,
count(b.c_guid) as bookings,
100.0 * count(b.c_guid) / count(*) as percent,
100.0 * count(b.c_guid) / first_value(count(b.c_guid)) over ( order by segment='control' desc, segment asc ) as comp
from mailing_tests
left join (
select distinct g.contact_guid as c_guid
from guest g
inner join booking
on booking.guid = g.booking_guid
where booking.book_date >= {{date_start}}
[[and booking.book_date < {{date_end}}]]
and booking.status in ('Booked')
) b
on mailing_tests.guid = b.c_guid
where {{project}}
group by segment
order by segment='control' desc, segment asc
'