Real Time SAP ABAP Internal Tables

1. what is an internal table?
   
2. how many type of internal tables are there?
   
3. what is the difference between hashed & sorted internal
   tables?
   
4. what is the difference between standard and sorted
   internal tables? (in performance wise)
   
5. Difference between internal table and a dictionary table?
   
6. can you create an internal table dynamically?(at run time)
   
7. what is the use of select for all entries in an internal
   table?
   
8. when you are using 2 internal table in program, you have
   decided to use for all entries statement to retrieve data
   but unfortunately there are no records in the first internal
   table. What will be the result? (2nd internal table contains
   records).
   
9. in a loop of an internal table, what is the use of at first &
   at last statements?
   
10. What is the use of at new statement?
    
11. what is the difference between at first & at new
    statements?
    
12. what is a binary search ? and how it is useful in a sorted
    internal table?
    
13. when do you need to create an internal table with header
    line ?and with out a header line?
    
14. what does it mean occurs 0 while creating an internal
    table?
    
15. what will happen if you don't give occurs clause while
    creating an internal table?
    
16. what is the difference between clear, delete & refresh
    with respect to an internal table?