Change History tracking and reporting - sql

Question

We're not allowed to use CDC.
We have a requirement to report changes made to a table, in the format of:
On [This Date], user [UserName] changed the field [FieldName] from
[OldValue] to [New Value]
My idea is to use an Update/Insert trigger on the table, call it TableA, and write the row to a new TableA_Tracking tablem which ahs the same columns, as well as a foreign key to the source table.
TableA has a 'LastUpdatedByUserId' as well as a 'LastUpdateDate' column.
Storing the data with the trigger is OK. However, I'm wondering if there is an efficient way to get the data back so that I can report it back to the application.
Is there a pattern I could follow for extracting the data into a table format, and return that to the UI for formatting?
I am thinking, something on the lines of:
WITH Track_CTE (
Placement_TrackID,
PlacementId,
PlacementEventId,
CarerId,
FosterCareAllowanceFlag,
InterstateAllowanceAmount,
FosterCareAllowanceReason,
FosterCareAllowanceDate,
InterstateAllowanceFlag,
LastUpdateUser,
LastUpdateDate
)
AS
(
SELECT
Placement_TrackID,
PlacementId,
PlacementEventId,
CarerId,
FosterCareAllowanceFlag,
InterstateAllowanceAmount,
FosterCareAllowanceReason,
FosterCareAllowanceDate,
InterstateAllowanceFlag,
LastUpdateUser,
LastUpdateDate
FROM
[Placement_Track]
)
SELECT *
FROM Track_CTE c1
LEFT JOIN Track_CTE c2
ON c2.Placement_TrackID = c1.Placement_TrackID - 1
Where Placement_Track is a table that is a direct copy of the source table, except for the PK (First column). The table is written to by a trigger on updates and inserts.
This then has a row of the updated version, and the previous version... and from there, maybe work out the changes? But, I may be way off track.
I'd filter, in the above example, on PlacementId, as that's the PK of the source table, so the selection would be more limited. Also, in this example, the only columns I am tracking are FosterCareAllowanceFlag, InterstateAllowanceAmount, FosterCareAllowanceReason, FosterCareAllowanceDate and InterstateAllowanceFlag.

Answer 1

Whenever a table row changes, old data is available within a trigger in the system temporary table ##deleted & new data is available from the table ##inserted.
So if Table X (id int, col1 varchar(5), col2 varchar(100)) contains:
id = 1, col1 = 'Code', col2 = 'Descrition', then this data is updated via:
UPDATE X set col2 = 'Description' WHERE id = 1;
table ##deleted contains id = 1, col1 = 'Code', col2 = 'Descrition'
table ##inserted contains id = 1, col1 = 'Code', col2 = 'Description'
you could figure out how many columns there are in the table total, (provided the name of the table is defined in a variable inside the trigger) using INFORMATION_SCHEMA.COLUMNS, and with this info, it should be no issue to loop through the columns of the table, comparing ##deleted with ##inserted to generate the audit data you require.