How to retrieve all process related case details from the Database?

Hello,

I have question regarding retrieval of all case details and variables from the database?
For example, if i use the overview page which consists of all the fields( with data filled) which i have used in the process , is it possible to retrieve the case data only for the overview page?
Once a process is executed and completed, do all the case variable values get stored in the database or does it get lost once the case is completed?
In case the details of all the variables used in the case are stored in the database, how do i retrieve them for a particular process? Is there any particular table where the data is pushed into and a particular database query to retrieve the same?

Any help would be really appreciated.

Regards,
Sanjeev