The concept of most BI tools is to take the date off line, such as to a data warehouse, and summarize it in ways that make it easy to query and get the results you need. Typically, the BI tool has no interaction with the transactional application. For the sake of the database, it's generally better to have some sort of copy or extract of the database for these chores which are query intensive. Databases such as MySQL can be configured for OLAP or OLTP depending on the use, but mixing of these functions is generally not a good idea unless your BI needs are very basic and can be delivered using standard graphs and queries. There are many good BI tools out there - most are expensive. But check out Tableau, which I think is open source or has a community edition.
