Eliminating duplicate rows with null values using with clause - sql

Question

How do we eliminate duplicates by only selecting those with values in a certain field using with clause statement?
Query is something like this:
with x as (--queries with multiple join tables, etc.)
select distinct * from x
Output below:
Com_no Company Loc Rewards
1 Mccin India 50
1 Mccin India
2 Rowle China 18
3 Draxel China 11
3 Draxel China
4 Robo UK
As you can see, I get duplicate records. I want to get rid of the null values that are NOT unique. That is to say, Robo is unique since it only has 1 record with a null value in Rewards, so I want to keep that.
I tried this:
with x as (--queries with multiple join tables, etc.)
select distinct * from x where Rewards is not null
And of course that wasn't right, since it also got rid of 4 Robo UK
Expected output should be:
1 Mccin India 50
2 Rowle China 18
3 Draxel China 11
4 Robo UK

Answer 1

The problem is you're calling those rows duplicates, but they're not duplicates. They're different. So what you want to do is exclude rows where Rewards is null UNLESS there aren't any rows with a not null value, and then select the distinct rows. So something like:
select distinct *
from x a
where Rewards is not null
or (Rewards is null and not exists (select 1 from x b where a.Com_no = b.Com_no
and b.Rewards is not null)
Now your Robo row will still be included as there isn't a row in x for Robo where Rewards is not null, but the rows for the other Companies with null Rewards will be excluded as there are not null rows for them.

Answer 2

This is a prioritization query. One method is to use row_number(). If you want only one value per Com_no/Company/Loc, then:
select x.*
from (select x.*,
row_number() over (partition by Com_no, Company, Loc order by Rewards nulls last) as seqnum
from x
) x
where seqnum = 1;
Or even:
select Com_no, Company, Loc, max(Rewards)
from x
group by Com_no, Company, Loc;