How to rebuild a record from a change log - sql

Question

I have a table of changes to an entity. I am trying to rebuild the data from the changes.
This is my Changes table:
CREATE TABLE Changes
(
Id IDENTITY,
RecordId INT,
Field INT,
Val VARCHAR(MAX),
DateOfChange DATETIME
);
Field column is a reference to what field changed, Val is the new value, RecordId is the Id of the record that changed. Ideally the Record table would contain the latest values but I am not that lucky. There are 10 different fields that changes are tracked, mostly dates but some other types are thrown in there.
This is my Record table:
CREATE TABLE Records
(
Id IDENTITY,
AUserGeneratedIdentifer VARCHAR(12)
)
I'd like to have a view to query by the rolled up values.
SELECT
AUserGeneratedIdentitfier, DateOpened, DateClosed, etc
FROM
RecordView
WHERE
AUserGeneratedIdentitfier = 'something'
I am trying to implemented it with CTEs but I am wondering if this is the correct way. I am using a CTE per field I am trying to get to.
WITH DateOpened AS
(
SELECT
RecordId, Val,
ROW_NUMBER() OVER (PARTITION BY RecordId ORDER BY DateOfChanged DESC) Rank
FROM
Changes
WHERE
FieldId = #DateOpenedId
) --- ... Repeat for every field
SELECT (my fields)
FROM Records
INNER JOIN <all ctes> on Record Id
But this method feels wrong to me, possibly due to my lack of SQL experience. Is there a better way that I am missing here? What are the performance implications of having multiple CTEs on the same table and joining with them?
Please excuse the hastily thrown together pseudo code, I hope it illustrates my problem accurately

Answer 1

I think you should be able to use a single ROW_NUMBER and pivot it as below.
DECLARE #Records TABLE (Id INT IDENTITY, AUserGeneratedIdentifer VARCHAR(12))
DECLARE #Changes TABLE (Id INT IDENTITY, RecordId INT, Field INT, Val VARCHAR(MAX), DateOfChange DATETIME);
INSERT INTO #Records (AUserGeneratedIdentifer)
VALUES ('qwer'), ('asdf')
INSERT INTO #Changes (RecordId, Field, Val, DateOfChange)
VALUES (1, 1, 'foo', '2021-01-01' ),
(2, 1, 'fooz', '2021-01-01' ),
(2, 2, 'barz', '2021-01-01' ),
(1, 2, 'bar', '2021-01-01' ),
(1, 1, 'foo2', '2021-01-02' ),
(2, 2, 'barz2', '2021-01-02' )
SELECT piv.RecordId, piv.[1], piv.[2]
FROM (
SELECT C.RecordId, C.Field, C.Val, ROW_NUMBER() OVER (PARTITION BY C.RecordId, C.Field ORDER BY C.DateOfChange DESC) RowNum
FROM #Changes C
) sub
PIVOT (
MAX(Val)
FOR Field IN ([1], [2])
) piv
WHERE piv.RowNum = 1