How to view a user's personal data after the user performs a login?
You might be able to use the Forena module (disclosure: I'm a co-maintainer) to build custom queries to retrieve the data directly from such database (of which its format can be MS SQL, MySql, Oracle, some PDO compliant database, etc). Think of those custom queries as standard SQL statements that fit your requirements (to retrieve the data). And combine this with the creation of some custom reports.

Those reports can then be shown in an appropriate page (with a specific path), or you could show them in a block, by using Forena's integration with the BEAN module.

PS: I'm assuming this question is about D7.