Actually I'm unable to understand the comments and answers properly. Problem is with the word "CLOBBER".....
Same here but after checking this http://en.wikipedia.org/wiki/Clobbering
, it kind of eased the question to understand.
Like it says c1 = c2 and c2 = c1, if we do the same in programming language like this
Dim a As Integer
Dim b As Integer
a = 1
b = 2
a = b
b = a
in the 5th line a = 2 and 6th line b is not 1 as a is already 2 so here the original value of a which was 1 is no longer in picture, so the b is written to b itself with its original value.
(i guess, i got this write... ;-) )
The first and the hardest SQL statement I have wrote- "select * from customers" - and I was happy and felt smart.