TSQL Update multiple columns with CASE but depending on a value - sql-server

Question

this is driving me a bit nuts. I'll explain a simplified version of my problem. I have two tables, source and destination:
CREATE TABLE AMG_TDest(
ID INT,
Value1 INT,
Value2 INT,
Value3 INT,
Value4 INT)
CREATE TABLE AMG_TSource(
ID INT,
RowNumber INT,
Value INT)
INSERT INTO AMG_TDest VALUES (1, 0, 0, 0, 0), (2, 0, 0, 0, 0)
INSERT INTO AMG_TSource VALUES (1, 1, 1), (1, 2, 2), (1, 3, 3), (1, 4, 4), (2, 1, 10), (2, 2, 20), (2, 3, 30), (2, 4, 40)
I want to update Value1, Value2, Value3 and Value4 in Destination table depending on TSource.RowNumber.
In the end what I want to get as a result is this on Destination table:
ID V1 V2 V3 V4
1 1 2 3 4
2 10 20 30 40
I tried this (with some variations)
UPDATE AMG_TDest
SET
Value1 = CASE WHEN S.RowNumber = 1 THEN COALESCE(S.Value, 0) ELSE Value1 END,
Value2 = CASE WHEN S.RowNumber = 2 THEN COALESCE(S.Value, 0) ELSE Value2 END,
Value3 = CASE WHEN S.RowNumber = 3 THEN COALESCE(S.Value, 0) ELSE Value3 END,
Value4 = CASE WHEN S.RowNumber = 4 THEN COALESCE(S.Value, 0) ELSE Value4 END
FROM ( SELECT * FROM AMG_TSource ) AS S
INNER JOIN AMG_TDest D ON D.ID = S.ID
It just updates the Value1 from first row and Value4 from last row. I've been battling with this for some hours now and I can't make it work. If anyone has suggestions I'm really thankful.

Answer 1

Here's a method using a PIVOT
;WITH cteX
AS(
SELECT PVT.ID
, PVT.Value4
, PVT.Value3
, PVT.Value2
, PVT.Value1
FROM
(
SELECT S.ID
, RN ='Value' + CAST(S.RowNumber AS varchar(10))
, S.[Value]
FROM dbo.AMG_TSource S
) X
PIVOT
(
MAX(Value) FOR RN IN ([Value1],[Value2],[Value3],[Value4])
) PVT
)
UPDATE D
SET D.Value1 = X.Value1
, D.Value2 = X.Value2
, D.Value3 = X.Value3
, D.Value4 = X.Value4
FROM
dbo.AMG_TDest D
INNER JOIN
cteX X ON X.ID = D.ID
The Pivot chamges the Source dataset like so
ID Value4 Value3 Value2 Value1
1 4 3 2 1
2 40 30 20 10
Then all you need to is then join on the ID column
for the update to the destination table