display oldest value with newest value at id level - sql

Question

I have a table that looks something like this where ids are displayed with old value with the new value (the one it just got changed into).
IF OBJECT_ID('tempdb.dbo.#TT','U')IS NOT NULL
DROP TABLE #TT;
SELECT *
INTO #TT
FROM (
SELECT 1 AS ID, 'A' AS OldValue, 'B' AS NewValue, CONVERT(DATE,'20190421') AS [Date]
UNION ALL
SELECT 1 AS ID, 'B' AS OldValue, 'C' AS NewValue, CONVERT(DATE,'20190423') AS [Date]
UNION ALL
SELECT 2 AS ID, 'D' AS OldValue, 'E' AS NewValue, CONVERT(DATE,'20190422') AS [Date]
UNION ALL
SELECT 3 AS ID, 'J' AS OldValue, 'K' AS NewValue, CONVERT(DATE,'20190422') AS [Date]
UNION ALL
SELECT 3 AS ID, 'K' AS OldValue, 'L' AS NewValue, CONVERT(DATE,'20190423') AS [Date]
UNION ALL
SELECT 3 AS ID, 'L' AS OldValue, 'M' AS NewValue, CONVERT(DATE,'20190424') AS [Date]
) T
;
I want to display each id and old value with newest value available for them. For example ID=1 and OldValue = A should display C or ID = 3 and OldValue = K should display M
I have tried to do recursive cte as follows:
WITH RecCTE AS (
SELECT ID, OldValue, NewValue
FROM #TT
UNION ALL
SELECT A.ID, B.OldValue, A.NewValue
FROM #TT A
INNER JOIN RecCTE B ON A.ID = B.ID AND B.NewValue = A.OldValue
)
SELECT *
FROM RecCTE
With that recursive query. I am getting some line correctly but I am also getting extra lines in between:
| ID | OldValue | NewValue |
|-----------|---------------|----------------|
| 1 | A | B |
| 1 | B | C |
| 2 | D | E |
| 3 | J | K |
| 3 | K | L |
| 3 | L | M |
| 3 | K | M |
| 3 | J | L |
| 3 | J | M |
| 1 | A | C |
I want to get results like this:
| ID | OldValue | NewValue |
|-----------|---------------|----------------|
| 1 | A | C |
| 1 | B | C |
| 2 | D | E |
| 3 | J | M |
| 3 | K | M |
| 3 | L | M |

Answer 1

I think taking the last row should work:
WITH RecCTE AS (
SELECT ID, OldValue, NewValue, 1 as lev
FROM #TT
UNION ALL
SELECT A.ID, B.OldValue, A.NewValue, lev + 1
FROM #TT A JOIN
RecCTE B
ON A.ID = B.ID AND B.NewValue = A.OldValue
)
SELECT *
FROM (SELECT r.*, ROW_NUMBER() OVER (PARTITION BY id, OldValue ORDER BY lev DESC) as seqnum
FROM RecCTE r
) r
WHERE seqnum = 1;

Answer 2

If the data works the way it looks to me like it works, the following will do it without using recursion:
;WITH cte as (
-- List of all, ordered by ID, with the most recent being the first listed
SELECT
ID
,NewValue
,row_number() over (partition by Id order by Date desc) Ranking
from #TT
)
select
tt.Id
,tt.OldValue
,cte.NewValue
from #TT tt
-- Join table to the "most recent" row for the ID
inner join cte
on cte.ID = tt.Id
and cte.Ranking = 1