SQL 服务器用列的长度替换NULL

Question

There is a table

foo   bar   id
foo1  bar1  NULL
foo2  bar2  NULL
foo2  bar2  NULL
foo3  bar3  NULL
foo4  bar4  NULL
foo4  bar4  NULL

I need to replace the NULL values with the length of the column like, 1,2,3 and so on

foo   bar   id
foo1  bar1  1
foo2  bar2  2
foo2  bar2  3
foo3  bar3  4
foo4  bar4  5
foo4  bar4  6

I have Googled but did not get how to make it

Answer 1

As commented by jarlh, it looks like you are trying to assign incremental numbers to column id , ordered by foo , then bar :

select 
    foo,
    bar,
    case when id is null then row_number() over(order by foo, bar) else id end id
from mytable

If you are looking for an update:

with cte as (
    select 
        foo,
        bar,
        id,
        row_number() over(order by foo, bar) rn
    from mytable
)
update cte set id = rn
where id is null