I did a similar thing with SQL Server using XML. I created views that would convert the XML value back to the correct SQL data type when querying the audit tabl

I did a similar thing with SQL Server using XML. I created views that would convert the XML value back to the correct SQL data type when querying the audit table. The view also Unions the audit data with the current data so that you could add the trigger at any time and the view would return the current data (the audit table only stores updates and deletes). One nice addition was saving the current user ID with all audit records, which I was able to get in the trigger by adding it to the db connection using CONTEXT_INFO().