I have a table “orders” in postgres with columns “offer_id” and “date”. I need to write a code which must fill in all empty cases in column “offer_id”, using the previous results. I try to use “lag” function but the problem is that it only manages with one single NULL but not several. How to fix that?

image here

I tried this

with orders as (
                  select 2 as offer_id, '2021-01-01'::date as date union all
                  select 3 as offer_id, '2021-01-02'::date as date union all
                  select null as offer_id, '2021-01-03'::date as date union all
                  select null as offer_id, '2021-01-04'::date as date union all
                  select null as offer_id, '2021-01-05'::date as date union all
                  select 4 as offer_id, '2021-01-07'::date as date union all
                  select 5 as offer_id, '2021-01-08'::date as date union all
                  select null as offer_id, '2021-01-09'::date as date union all
                  select 8 as offer_id, '2021-01-10'::date as date union all
                  select 9 as offer_id, '2021-01-11'::date as date union all
                  select null as offer_id, '2021-01-12'::date as date union all
                  select null as offer_id, '2021-01-13'::date as date union all
                  select 13 as offer_id, '2021-01-14'::date as date union all
                  select 13 as offer_id, '2021-01-15'::date as date union all
                  select null as offer_id, '2021-01-16'::date as date 
                  )
select *, CASE WHEN offer_id IS NULL 
THEN LAG(offer_id) OVER (ORDER BY date) ELSE offer_id END updated_offer_id 
from orders