track change in sql row for update - mysql

Question

I've a java program to update a SQL table (id, name, status). Entire table is updated with same data or some changed data. How can I track if a row is same like it was before update or it has some modified data? id will be always same, only small typo on name. I just want to check on next update if name is modified. In this case the status field should be changed from 'same' to 'modified'. Will timestamp solve my issue? Please help.

Answer 1

1 - If you are looking to audit the table (inserts, updates, deletes), look at my how to prevent unwanted transactions slide deck w/code - http://craftydba.com/?page_id=880.
SEE CODE AT END!
The trigger that fills the audit table can hold information from multiple tables since the data is saved as XML. Therefore, you can un-delete if necessary. It tracks who and what made the change.
2 - If you are never going to purge the data from the audit table, why not mark the row as deleted but keep it for ever?
Many systems like people soft use effective dating to show if a record is no longer active. In the BI world this is called a type 2 dimensional table (slowly changing dimensions).
See the data warehouse institute article. http://www.bidw.org/datawarehousing/scd-type-2/
Each record has a begin and end date. All active records have a end date of null.
3 - Micorsoft SQL Server introduced the change data capture feature. While this tracks data change using a LOG reader after the fact, it lacks things like who and what made the change.
Again, all the above solutions work. I am partial to my solution!
Sincerely
John
The Crafty DBA
--
-- 7 - Auditing data changes (table for DML trigger)
--
-- Delete existing table
IF OBJECT_ID('[AUDIT].[LOG_TABLE_CHANGES]') IS NOT NULL
DROP TABLE [AUDIT].[LOG_TABLE_CHANGES]
GO
-- Add the table
CREATE TABLE [AUDIT].[LOG_TABLE_CHANGES]
(
[CHG_ID] [numeric](18, 0) IDENTITY(1,1) NOT NULL,
[CHG_DATE] [datetime] NOT NULL,
[CHG_TYPE] [varchar](20) NOT NULL,
[CHG_BY] [nvarchar](256) NOT NULL,
[APP_NAME] [nvarchar](128) NOT NULL,
[HOST_NAME] [nvarchar](128) NOT NULL,
[SCHEMA_NAME] [sysname] NOT NULL,
[OBJECT_NAME] [sysname] NOT NULL,
[XML_RECSET] [xml] NULL,
CONSTRAINT [PK_LTC_CHG_ID] PRIMARY KEY CLUSTERED ([CHG_ID] ASC)
) ON [PRIMARY]
GO
-- Add defaults for key information
ALTER TABLE [AUDIT].[LOG_TABLE_CHANGES] ADD CONSTRAINT [DF_LTC_CHG_DATE] DEFAULT (getdate()) FOR [CHG_DATE];
ALTER TABLE [AUDIT].[LOG_TABLE_CHANGES] ADD CONSTRAINT [DF_LTC_CHG_TYPE] DEFAULT ('') FOR [CHG_TYPE];
ALTER TABLE [AUDIT].[LOG_TABLE_CHANGES] ADD CONSTRAINT [DF_LTC_CHG_BY] DEFAULT (coalesce(suser_sname(),'?')) FOR [CHG_BY];
ALTER TABLE [AUDIT].[LOG_TABLE_CHANGES] ADD CONSTRAINT [DF_LTC_APP_NAME] DEFAULT (coalesce(app_name(),'?')) FOR [APP_NAME];
ALTER TABLE [AUDIT].[LOG_TABLE_CHANGES] ADD CONSTRAINT [DF_LTC_HOST_NAME] DEFAULT (coalesce(host_name(),'?')) FOR [HOST_NAME];
GO
--
-- 8 - Make DML trigger to capture changes
--
-- Delete existing trigger
IF OBJECT_ID('[ACTIVE].[TRG_FLUID_DATA]') IS NOT NULL
DROP TRIGGER [ACTIVE].[TRG_FLUID_DATA]
GO
-- Add trigger to log all changes
CREATE TRIGGER [ACTIVE].[TRG_FLUID_DATA] ON [ACTIVE].[CARS_BY_COUNTRY]
FOR INSERT, UPDATE, DELETE AS
BEGIN
-- Detect inserts
IF EXISTS (select * from inserted) AND NOT EXISTS (select * from deleted)
BEGIN
INSERT [AUDIT].[LOG_TABLE_CHANGES] ([CHG_TYPE], [SCHEMA_NAME], [OBJECT_NAME], [XML_RECSET])
SELECT 'INSERT', '[ACTIVE]', '[CARS_BY_COUNTRY]', (SELECT * FROM inserted as Record for xml auto, elements , root('RecordSet'), type)
RETURN;
END
-- Detect deletes
IF EXISTS (select * from deleted) AND NOT EXISTS (select * from inserted)
BEGIN
INSERT [AUDIT].[LOG_TABLE_CHANGES] ([CHG_TYPE], [SCHEMA_NAME], [OBJECT_NAME], [XML_RECSET])
SELECT 'DELETE', '[ACTIVE]', '[CARS_BY_COUNTRY]', (SELECT * FROM deleted as Record for xml auto, elements , root('RecordSet'), type)
RETURN;
END
-- Update inserts
IF EXISTS (select * from inserted) AND EXISTS (select * from deleted)
BEGIN
INSERT [AUDIT].[LOG_TABLE_CHANGES] ([CHG_TYPE], [SCHEMA_NAME], [OBJECT_NAME], [XML_RECSET])
SELECT 'UPDATE', '[ACTIVE]', '[CARS_BY_COUNTRY]', (SELECT * FROM deleted as Record for xml auto, elements , root('RecordSet'), type)
RETURN;
END
END;
GO

Answer 2

SQL Server doesn't have versioning on the table level. If you want to track difference between two field you have at least two options:
Control from your Java application - do pre-update check in your update method.
Control from SQL Server - write trigger again for pre-update check
You can also create suplimentary field where Version number will be kept

Answer 3

Yes you can use time stamp.
By using time stamp, you can find out the latest entry into the table and by using Order by timestamp in the query,you can get the latest and set the status based on corresponding value

Answer 4

It depends on how much information you need. If all you care about is whether the record has ever been modified, you can use created_when and updated_when fields. If the latter is greater than the former, it's been updated.
If you want to know what fields have been updated, you have to log the changes. The details depend on your requirements. If you need to log changes, a trigger is the best way to do it.