SQL Query to get PO Change and Approval History

I am building an audit report to get a clear view of the PO Changes and Approval History. There is not much that I can find and the query I am using does not seem to be correct. I have added my very basic query below. If you know, how can I get this data or what can I do to correct my query, I would highly appreciate it.

Data I am looking for - Who created the PO, Who approved it, who made a change, who approved it and what was reason for making that change.

/* PO Approval History */