If same Value Occur Update status as 2 - sql

Question

I have a table like by following..
ID CustId CustName Status
1 a1 A NULL
2 a1 A NULL
3 a2 B NULL
4 a3 B NULL
5 a4 C NULL
6 a4 C NULL
7 a5 D NULL
8 a6 E NULL
I want to update the status = 2 when custid occurs 2nd time and I need output following like this...
ID CustId CustName Status
1 a1 A 1
2 a1 A 2
3 a2 B 1
4 a3 B 1
5 a4 C 1
6 a4 C 2
7 a4 D 2
8 a6 E 1
Now I am using the following query to update the status
update #tablename
set status= 2
where Custid in
(
select * from
(
select Custid
from #tablename
group by Custid
having count(*)> 1
) a
)
but the above query is updating the status=2 when count(custid)>1
I don't want to update first row..

Answer 1

CREATE TABLE #UserCompany
([ID] int, [CustId] varchar(2), [CustName] varchar(1), [Status] int)
;
INSERT INTO #UserCompany
([ID], [CustId], [CustName], [Status])
VALUES
(1, 'a1', 'A', null),
(2, 'a1', 'A', null),
(3, 'a2', 'B', null),
(4, 'a3', 'B', null),
(5, 'a4', 'C', null),
(6, 'a4', 'C', null),
(7, 'a4', 'D', null),
(8, 'a6', 'E', null)
;
select *,row_number() over (partition by [CustId] order by [ID]) as rn from #UserCompany
with cte as
(
select *,row_number() over (partition by [CustId] order by [ID]) as rn from #UserCompany)
update cte
set [Status]=case when rn > 1 then 2 else 1 end
or
UPDATE b
SET b.[Status] = a.[Status]
FROM #UserCompany a
INNER JOIN (select *,row_number() over (partition by [CustId] order by [ID]) as rn from #UserCompany) b
ON a.id = b.id

Answer 2

Intro
Easiest way to solve this would be with a subquery.
So for every row, you generate a subquery returning only one value.
This subquery will basically count the number of records ( for that customer id), that have an ID >= the current customer id.
Code
UPDATE UserCompany
SET
UserCompany.status = temp.status
FROM usercompany AS u
INNER JOIN
( SELECT ID,
CustID,
CustName,
(SELECT count(*)
FROM UserCompany t
WHERE t.custId = u.custId
AND t.ID <= u.id ) AS status
FROM UserCompany u ) AS TEMP ON temp.ID = u.ID;
select * from UserCompany;
Update 1: Only update records where previous same cust instance-count >= 2
UPDATE UserCompany
SET
UserCompany.status = temp.status
FROM usercompany AS u
INNER JOIN
( SELECT ID,
CustID,
CustName,
(SELECT count(*)
FROM UserCompany t
WHERE t.custId = u.custId
AND t.ID <= u.id ) AS status
FROM UserCompany u ) AS TEMP ON temp.ID = u.ID AND TEMP.STATUS >=2;
select * from UserCompany;
Update 2: Same as Update 1, but set 2 instead of actual count
(same as above but inserts 2 instead of real count)
UPDATE UserCompany
SET
UserCompany.status = temp.insert_status
FROM usercompany AS u
INNER JOIN
( SELECT ID,
CustID,
CustName,
2 as insert_status,
(SELECT count(*)
FROM UserCompany t
WHERE t.custId = u.custId
AND t.ID <= u.id ) AS status
FROM UserCompany u ) AS TEMP ON temp.ID = u.ID AND TEMP.STATUS >=2;
select * from UserCompany;