RE: I need a report showing user who posted and user who approved
The GL20000 & GL30000 tables both have APRVLUSERID and APPRVLDT (id & date). Those are the open year & historical year GL transaction tables.
Since you are on GP2015, you can easily add these fields to your SmartLists, using the SmartList Designer. Since you want this information in Excel, another option would be to create a refreshable Excel report by creating & using an .odc connection.
If you're unsure how to begin with either of these, here is a link to an introductory video on Designer: https://www.youtube.com/watch?v=Vz-d6RC2SYI
And here is a link that talks about publishing Designer reports to Excel: https://www.youtube.com/watch?v=C9h_3a_eumk
FYI, there are tons of ways to create refreshable Excel reports that are connected to your GP data. This video is one option of many.
Good luck, and have fun! Designing custom reports is one of my favoritest things. (bad grammar intentional!)
Side note: I actually found 16 tables in my TWO database with the APRVLUSERID column, using this script:
select TABLE_NAME from information_schema.columns
where COLUMN_NAME = 'APRVLUSERID'
order by TABLE_NAME