How to set Conditional Row Number by specific values from the table - sql

Question

I have a query that returns table and based on value (if that exists) I want to set row_number.
I have some solution but it looks long and I think could be easier and less code (best option) to handle it. Below sample with expected results:
If query returns Client with NULL:
----------------------
Process | Client|
A | NULL |
A | B |
A | B |
A | B |
A | C |
A | C |
A | C |
OutPut should be:
----------------------
Process | Client| RowNumber
A | NULL | 1
A | B | 2
A | B | 3
A | B | 4
A | C | 2
A | C | 3
A | C | 4
If query returns without NULL:
----------------------
Process | Client|
A | B |
A | B |
A | B |
A | C |
A | C |
A | C |
OutPut should be:
----------------------
Process | Client| RowNumber
A | B | 1
A | B | 2
A | B | 3
A | C | 1
A | C | 2
A | C | 3

Answer 1

I'm not sure if NULL should always be treated as 'B', but you need to handle that:
select t.* ,
row_number() over (partition by process, coalesce(client, 'B') order by (select null))
from t
where client is not null;
Oh, I see, you are not setting the NULL to 'B' but adding the number of NULLs to the other values. That is also quite simple:
select t.* ,
(row_number() over (partition by process, client order by (select null)) +
(case when client is null then 0
else sum(case when client is null then 1 else 0 end) over ()
end)
)
from t
where client is not null;

Answer 2

dbfiddle
DROP TABLE if exists mytable;
CREATE TABLE mytable(Process char(1), Client char(1));
INSERT INTO mytable values
('A',null),
('A','B'),
('A','B'),
('A','B'),
('A','C'),
('A','C'),
('A','C');
-- with a NULL value
select
Process,
Client,
ROW_NUMBER() OVER (partition by process,Client order by (select null))+CASE WHEN Client is null THEN 0 else 1 end R
from mytable;
-- without a NULL value
select
Process,
Client,
ROW_NUMBER() OVER (partition by process,Client order by (select null)) R
from mytable
where not client is null;

Answer 3

…
declare #t table(process varchar(10), client varchar(10));
insert into #t(process, client)
values
('A', null),
('A', 'B'),('A', 'B'),('A', 'B'),
('A', 'C'),('A', 'C'),
('A', ''), ('A', ''), ('A', ' '), ('A', ' '),
('A', 'ZXY'), ('A', 'ZXY'),
('X', 'B'),('X', 'B'),('X', 'B'),
('X', 'C'),('X', 'C');
select *,
row_number() over(partition by process,client order by client)
--if there is a null client per process then add 1 to every non null client
+ case when client is not null and min(case when client is null then 0 else 1 end) over(partition by process) = 0 then 1 else 0 end
--+ case when client is not null and min(isnull(ASCII(client+'.'), 0)) over(partition by process) = 0 then 1 else 0 end
as rownumber
from
(
select *
from #t
--where client is not null
) as t;