Windowed functions can only appear in the SELECT or ORDER BY clauses-update in cursor

Question

Declare @Customerid int 
DECLARE ChangeCustomerName CURSOR FOR 
select customerid from customer 
OPEN ChangeCustomerName
FETCH NEXT FROM ChangeCustomerName into @Customerid
WHILE @@fetch_status = 0
BEGIN

  update customer set customername ='Customer'
    +convert (varchar(10),ROW_NUMBER() OVER(ORDER BY customerid ASC)) 
    where customerid=@Customerid

   FETCH NEXT FROM ChangeCustomerName into @Customerid
END
close ChangeCustomerName
deallocate ChangeCustomerName

Windowed functions can only appear in the SELECT or ORDER BY clauses-update in cursor

Answer 1

You seem to be trying to set customer names to sequential values. For this purpose, you don't need a cursor! Just something like this:

with toupdate as (
      select c.*, row_number() over (order by customerid) as seqnum
      from customer c
     )
update toupdate
    set customername = 'Customer' + convert(varchar(10), seqnum);

You should avoid cursors whenever you can. Set-based operations are more efficient and often result in simpler code.