IF Else or Case Function for SQL select problem - sql

Question

Hi I would like to make a select expression using case or if/else which seems to be a simple solution from logic perspective but I can't seem to get it to work. Basically I am joining against two table here, the first table is customer record with date filter called min_del_date and then the second table for the model scoring table with BIN and update_date parameters.
There are two logics I want to display
Picking the model score that was the month before min_del_date
If model score month before delivery is greater than 50 (Bin > 50) then pick the model score for same month as min_del_date
My 1st logic code is below
with cust as (
select
distinct cust_no, max(del_date) as del_date, min(del_date) as min_del_date, (EXTRACT(YEAR FROM min(del_date)) -1900)*12 + EXTRACT(MONTH FROM min(del_date)) AS upd_seq
from customer.cust_history
group by 1
)
,model as (
select party_id, model_id, update_date, upd_seq, bin, var_data8, var_data2
from
(
select
party_id, update_date, bin, var_data8, var_data2,
(EXTRACT(YEAR FROM UPDATE_DATE) -1900)*12 + EXTRACT(MONTH FROM UPDATE_DATE) AS upd_seq,
dense_Rank() over (partition by (EXTRACT(YEAR FROM UPDATE_DATE) -1900)*12 + EXTRACT(MONTH FROM UPDATE_DATE) order by update_date desc) as rank1
from
(
select party_id,update_date, bin, var_data8, var_data2
from model.rpm_model
group by party_id,update_date, bin, var_data8, var_data2
) model
)model_final
where rank1 = 1
)
-- Add model scores
-- 1st logic Picking the model score that was the month before delivery date
select *
from
(
select cust.cust_no, cust.del_date, cust.min_del_date, model.upd_seq, model.bin
from cust
left join cust
on cust.cust_no = model.party_id
and cust.upd_seq = model.upd_seq + 1
)a
Now I am struggling in creating the 2nd logic in the same query?.. any assistance would be appreciated
cust table
cust_no
min_del_date
upd_seq
123
2021-01-11
1453
234
2020-06-29
1446
456
2020-07-20
1447
model table
party_id
update_date
upd_seq
BIN
123
2020-11-30
1451
22
123
2020-12-25
1452
54
123
2020-01-11
1453
14
234
2020-05-23
1445
76
234
2020-06-18
1446
48
234
2020-07-23
1447
12
456
2020-06-18
1446
23
456
2020-07-23
1447
39
456
2020-08-21
1448
21
desired results
cust_no
min_del_date
model.upd_seq
update_date
BIN
123
2021-01-11
1453
2020-01-11
14
234
2020-06-29
1446
2020-06-18
48
456
2020-07-20
1446
2020-06-18
23
Update
I managed to find the solution by myself, thanks for everyone who has attending this question. The solution is per below
select a.cust_no, a.del_date, a.min_del_date, b.update_date, b.upd_seq, b.bin
from
(
select cust.cust_no, cust.del_date, cust.min_del_date,
CASE WHEN model.BIN <=50 THEN model.upd_seq WHEN BIN > 50 THEN model.upd_seq +1 ELSE NULL END as upd_seq
from cust
inner join model
on cust.cust_no = model.party_id
and cust.upd_seq = model.upd_seq + 1
)a
inner join model b
on a.cust_no = b.party_id
and a.upd_seq = b.upd_seq