Tracking data changes

Dear experts,

I need to track all data changes in certain tables of my database and store information about the changes in a separate table, changelog.
I guess I should do it using triggers, but maybe you could tell how the trigger that could do that should look?
The changelog table has the following fields: Table (that holds table name where the change happened), Field (where the data was changed), Key (of the modified record), OrigValue, NewValue, UpdateTime, UserName.

Thanks.
tantormediaAsked:
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wolfgang_93Connect With a Mentor Commented:
In a default installation of MySQL, all commands are logged to a file (in the case of a
Linux install, the file has a name like .mysql_history).

Rather than set up a trigger -- which will cause a lot of extra activity in the database --
you could instead write a little script to periodically read and parse the contents of the
file and load information of interest to a MySQL table.

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sammySeltzerCommented:
this link has all the info you need. Scroll all the way down.

http://www.sqlservercentral.com/Forums/Topic294216-314-1.aspx#bm299093

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sammySeltzerCommented:
This is the complete working solution you can modify for your needs.

If you get hung, please post back where you need help.

CREATE TABLE [dbo].[Audit](
[AuditId] [bigint] IDENTITY(1,1) NOT NULL,
[TableName] [varchar](128) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[DateCreated] [datetime] NULL DEFAULT (getdate()),
[UserId] [int] NULL,
[SystemUser] [varchar](80) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[Operation] AS (case when [OldValue] IS NULL then 'Insert' else case when [NewValue] IS NULL then 'Delete' else 'Update' end end),
[OldValue] [xml] NULL,
[NewValue] [xml] NULL,
[OldBinaryValue] [varbinary](max) NULL,
[NewBinaryValue] [varbinary](max) NULL
)


CREATE TABLE [dbo].[AuditTable](
[TableName] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[IdentityColumnName] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
[UserIdColumnName] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
CONSTRAINT [PK_AuditTable] PRIMARY KEY CLUSTERED
(
[TableName] ASC
)


create proc [dbo].[SaveAudit]
@OldValues xml,
@NewValues xml

as

Declare @TableName varchar(128), @SystemUser varchar(80), @UserId int,
@ColumnName varchar(128), @Operation varchar(10), @sql varchar(1000)

SELECT @SystemUser=system_user

SELECT @TableName=object_name(resource_associated_entity_id)
FROM sys.dm_tran_locks
WHERE request_session_id = @@spid and resource_type = 'OBJECT'

Insert Into Audit (TableName, UserId, SystemUser, OldValue, NewValue)
Values (@TableName, null, @SystemUser, @OldValues, @NewValues)
go


CREATE proc [dbo].[GetAuditInfo]
@TableName varchar(128),
@StartDate datetime,
@EndDate datetime
as

set nocount on

Declare @x int, @max int, @sql varchar(4000), @ColumnName varchar(200)
set @x=1
set @sql=''

SELECT @max=count(c.[name])
FROM sys.all_columns c
INNER JOIN sys.all_objects o ON c.object_id = o.object_id
INNER JOIN sys.types t ON c.system_type_id = t.system_type_id
WHERE o.[name] = @TableName AND o.[type] = 'U'

while (@x <= @max)
Begin

SELECT @ColumnName=c.[name]
FROM sys.all_columns c
INNER JOIN sys.all_objects o ON c.object_id = o.object_id
INNER JOIN sys.types t ON c.system_type_id = t.system_type_id
WHERE o.[name] = @TableName and c.column_id=@x AND o.[type] = 'U'

set @sql=@sql+'v.value(''@'+@ColumnName+''', ''varchar(8000)'') as '+@ColumnName
if @x<@max
set @sql=@sql+', '

set @x=@x+1
End

Declare @sql2 varchar(8000)

set @sql2='SELECT TableName, DateCreated, SystemUser, Operation,'+@sql+
' Into ##340834audit FROM Audit CROSS APPLY OldValue.nodes(''/deleted'') x(v)
Where TableName='''+@TableName+''''

exec(@sql2)
set @sql2=''
set @sql2='Insert Into ##340834audit SELECT TableName, DateCreated, SystemUser, Operation,'+@sql+
' FROM Audit CROSS APPLY NewValue.nodes(''/inserted'') x(v)
Where TableName='''+@TableName+''''

exec(@sql2)

select * from ##340834audit Order By TableName, DateCreated, SystemUser, Operation
drop table ##340834audit
go


And finally.....a generic audit trigger for your tables

Create trigger [dbo].[AuditYourTable] on [dbo].[YourTable]
for insert, update, delete
as
declare @i xml, @d xml
set @i = (select * from inserted for xml auto)
set @d = (select * from deleted for xml auto)
exec SaveAudit @d, @i
GO
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tantormediaAuthor Commented:
sammySeltzer,

Thank you very much. But is it really MySql? Looks like MS SQL Server syntax to me.
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sammySeltzerCommented:
Oops, my bad.

I am sorry I thought it was sql server.

Sorry about that.

I am not too good with MySQL but let me see what i can do.
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sammySeltzerConnect With a Mentor Commented:
However, should decide is still your choice, here is information I googled up that looks closer to what you are looking for.

I have also included the link so you can understand what they did and *how* they did it.

Hope this helps you.

http://codespatter.com/2008/05/06/how-to-use-triggers-to-track-changes-in-mysql/


DROP TRIGGER IF EXISTS history_trigger $$
 
CREATE TRIGGER history_trigger
BEFORE UPDATE ON clients
    FOR EACH ROW
    BEGIN
        IF OLD.first_name != NEW.first_name
        THEN
                INSERT INTO history_clients
                    (
                        client_id    ,
                        col          ,
                        value        ,
                        user_id      ,
                        edit_time
                    )
                    VALUES
                    (
                        NEW.client_id,
                        'first_name',
                        NEW.first_name,
                        NEW.editor_id,
                        NEW.last_mod
                    );
        END IF;
 
        IF OLD.last_name != NEW.last_name
        THEN
                INSERT INTO history_clients
                    (
                        client_id    ,
                        col          ,
                        value        ,
                        user_id      ,
                        edit_time
                    )
                    VALUES
                    (
                        NEW.client_id,
                        'last_name',
                        NEW.last_name,
                        NEW.editor_id,
                        NEW.last_mod
                    );
        END IF;
 
    END;
$$
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tantormediaAuthor Commented:
Thanks.
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