Insert only modified values and column names into a table - sql

Question

I have a sql server 2012 database. In which i have a changeLog table that contains
TableName, ColumnName, FromValue and ToValue columns. Which will be used to keep track of modified columns and data.
So if any update occur through application then only modified columns should insert into this table with its new and old value.
Can anyone help me in this.
For Example:
If the procedure updates all columns of property table (propertyName, address)
then if user update propertyName (but update also contains address column but with no data change) then only propertyName and its data will be inserted into ChangeLog table not address column and its data because address data does not contains any data change.

Answer 1

IF there is no other auditing requirement at all - you would not be thinking about Auditing in any way without this - then OK, go for it. However this is a very limited use of Auditing: User X changed this field at time Y. Generally this is interesting as part of a wider question: what did user X do? What happened to that customer data in the database to end up the way it is now?
Questions like that are harder to answer if you have the data structure you propose and would be quite onerous to reconstruct. My usual approach would be as follows. Starting from a base table like so (this from one of my current projects):
CREATE TABLE [de].[Generation](
[Id] [int] IDENTITY(1,1) NOT NULL,
[LocalTime] [datetime] NOT NULL,
[EntityId] [int] NOT NULL,
[Generation] [decimal](18, 4) NOT NULL,
[UpdatedAt] [datetime] NOT NULL CONSTRAINT [DF_Generation_UpdatedAt] DEFAULT (getdate()),
CONSTRAINT [PK_Generation] PRIMARY KEY CLUSTERED
(
[Id] ASC
)
(I've excluded FK definitions as they aren't relevant here.)
First create an Audit table for this table:
CREATE TABLE [de].[GenerationAudit](
[AuditId] int identity(1, 1) not null,
[Id] [int] NOT NULL,
[LocalTimeOld] [datetime] NULL,
[EntityIdOld] [int] NULL,
[GenerationOld] [decimal](18, 4) null,
[UpdatedAtOld] [datetime] null,
[LocalTimeNew] [datetime] null,
[EntityIdNew] [int] null,
[GenerationNew] [decimal](18, 4) null,
[UpdatedAtNew] [datetime] NOT NULL CONSTRAINT [DF_GenerationAudit_UpdatedAt] DEFAULT (getdate()),
[UpdatedBy] varchar(60) not null
CONSTRAINT [PK_GenerationAudit] PRIMARY KEY CLUSTERED
(
[AuditId] ASC
)
This table has an *Old and a *New version of each column that can't change. The Id, being an IDENTITY PK, can't change so no need for an old/new. I've also added an UpdatedBy column. It also has a new AuditId IDENTITY PK.
Next create three triggers on the base table: one for INSERT, one for UPDATE and one for DELETE. In the Insert trigger, insert a row into the Audit table with the New columns selected from the inserted table and the Old values as null. In the UPDATE one, the Oldvalues come from the deleted and the new from the inserted. In the DELETE trigger, old from from deleted and the new are all null.
The UPDATE trigger would look like this:
CREATE TRIGGER GenerationAuditUpdate
ON de.Generation
AFTER UPDATE
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
insert into de.GenerationAudit (Id, LocalTimeOld, EntityIdOld, GenerationOld, UpdatedAtOld,
LocalTimeNew, EntityIdNew, GenerationNew, UpdatedAtNew,
UpdatedBy)
select isnull(i.Id, d.Id), d.LocalTime, d.EntityId, d.Generation, d.UpdatedAt,
i.LocalTime, i.EntityId, d.Generation, getdate(),
SYSTEM_USER)
from inserted i
full outer join deleted d on d.Id = i.Id;
END
GO
You then have a full before/after picture of each change (and it'll be faster than seperating out diffs column by column). You can create views over the Audit table to get entries where the Old value is different to the new, and include the base table Id (which you will also need in your structures!), the user who did it, and the time they did it (UpdatedAtNew).
That's my version of Auditing and it's mine!