Forum OpenACS Q&A: Re: OLAP, OACS and nsJava
Excel can create pivot tables from arbitrary ODBC sources. If you have the pg odbc driver, and access from the user's desktop to the web site, you can do this without OLAP.
There are typically two problems with this approach if it's a large amount of data - security and bandwidth
Normally you would deploy your web app somewhere on the 'net where you would prefer not to grant direct database access. Tech savvy end-users could do ssh tunnelling, or you could set up some similarly-encrypted VPN between end-user desktop and database server, but the tried-and-true way to go is to dump and load your production database to a reporting server that's on the same lan as the end user. That way even if you have a huge amount of data going back and forth between db and server, it's going across a 100MBit lan, and not the internet.