Updating records using self join or row number function

Question

IF OBJECT_ID('tempdb..#Temp') IS NOT NULL DROP TABLE #Temp
GO
CREATE TABLE #Temp
ID INT
, CYear INT
, Val INT
, Descrp Varchar(10) NULL
, Cd INT
, ToBeUpdated Varchar(5) NULL
INSERT INTO #Temp
ID
, CYear
, Val
, Descrp
, Cd
, ToBeUpdated
SELECT 2014, 2013, 111, 'ABC', 2, NULL
UNION
SELECT 2014, 2014, 111, 'XYZ', 2, NULL
UNION
SELECT 2014, 2014, 222, 'TTT', 3, NULL
UNION
SELECT 2014, 2013, 333, 'ZZZ', 4, NULL
UNION
SELECT 2014, 2014, 333, 'VVV', 5, NULL
SELECT * FROM #Temp
ORDER BY Val, CYear
All, I have the above #table. You'll notice that there are duplicate values in "Cd" column i.e. "Cd=2".
If the values in ID, Val and Cd are same then, I want to update the "CodeFlag" column for those records with "Descrp" column of
the recent CYear. So, my "ToBeUpdated" column would have a value of "XYZ" for both the records where Cd=2 (Since, XYZ is the Descrp for CYear 2014(the latest one))
Also, if the values in ID and Val column are same but values in "Cd" is different, then ToBeUpdated = Descrp of that particular record. In my case the "ToBeUpdated" value for Cd=4 would be "ZZZ" and for Cd=5, it would be "VVV"
since the ID and Val column values are same for those records. Let me know if you have any questions.

Answer 1

IF OBJECT_ID('tempdb..#Temp') IS NOT NULL DROP TABLE #Temp
GO
CREATE TABLE #Temp
ID INT , CYear INT , Val INT , Descrp Varchar(10) NULL , Cd INT , ToBeUpdated Varchar(5) NULL)
INSERT INTO #Temp
ID , CYear , Val , Descrp , Cd , ToBeUpdated)
SELECT 2014, 2013, 111, 'ABC', 2, NULL
UNION
SELECT 2014, 2014, 111, 'XYZ', 2, NULL
UNION
SELECT 2014, 2014, 222, 'TTT', 3, NULL
UNION
SELECT 2014, 2013, 333, 'ZZZ', 4, NULL
UNION
SELECT 2014, 2014, 333, 'VVV', 5, NULL
;with mycte as (SELECT *, row_number() Over(partition By ID, Val , Cd order by CYear DESC) rn
, row_number() Over(partition By ID, Val order by Descrp) rn1
FROM #Temp)
SELECT m1.ID ,m1.CYear,m1.Val,m1.Descrp , ToBeUpdated=d.descrp from mycte m1
Cross apply (Select Top 1 descrp from mycte m2 WHERE m2.id=m1.ID AND m1.Val=M2.Val AND m1.cd=m2.cd AND m1.rn>=m2.rn) d(descrp)