Few Queries (Basic-Level)

Hi All,

I am having few questions on Basic ABAP Programing

1) Selection Screen:

When i am at selection screen and if i press Cancel, it will take me to the list.For Eg if AT Start of selection, i am selecton data from database and writing to list, so even if user press cancel at selection screen , the query will be executed. How should we handle it?

2) In BDC, what is the exact difference between input session and call transaction. I am able to keep both in sessions and get the logs. I am able to view all the facilities in call transaction that are offered by input session. So, when should we go for waht and what is the exact difference between two.

Regards

Mitesh