How to assign integer values to based on id in SQL Server

I have a table like this:

id	value
15	a
15	b
18	c
19	d
20	e
20	f

I want to create a select query with replaces the id value with integers starting from 1.

id	value
1	a
1	b
2	c
3	d
4	e
4	f

This is my expectation. I am using SQL Server 2019.

Answer

We can try an updateable CTE with the help of DENSE_RANK:

WITH cte AS (
    SELECT *, DENSE_RANK() OVER (ORDER BY id) dr
    FROM yourTable
)

UPDATE cte
SET id = dr;