[otrs] SQL query for first response time and resolution time

Hello everybody, I want to build a report showing first response time and resolution time. The stat module doesn't seem to be able to do this. So, I started using an external reporting tool. The hardest part is to build the SQL query. Can anybody help me finding these informations in the database ? Do I have to compute these informations from "start" and "end" fields, or is the data stored in the database (maybe the <ticket> table) ? Thank you for your help. Regards, Régis