Some database related Questions

Question

1.Why using Index improve the performance , how will the data from the database is placed in the buffer ( as we see in the table or linear as per the buffer size)??
2. What happens when we create index for all the field, even it becomes like sequential read the performance will be improved right?
3. When a select statement is triggered, the corresponding table will come to buffer (if it is fully buffered) and the few records as per the given where condition is extracted adn placed Where?
4. I created a Ztable with three field numeric A , B and TOTAL and I am maintaining table maintence, so when ever i enter in SM30 field   A and B, TOTAL should be the appended automatically as the sum of a and b.whether is is possible how?
5.What is Composite Key? with a real time example?
regards,
Prabhu
POINTS ASSURED.

Answer 1

hi
when creating table primary key creates automatically
secondary index to be create according to user requirement
to resolve u r doubt simply create a select statement with where condition with non primary key field it wont fetch data if u create secondary index it will fetch data
buffered tables will be placed in apllication server ram
compositekey means combination of two primary keys
reward if u fin useful
regards
Nagesh .Paruchuri