Statistics collection - forum topic by Fractals

I have few doubts regarding statistics collection.
 
1. Does the order of columns used in collect stats command important? 
2. Consider the following scenario 
 
Table A joins with Table B based on Col1 and Col2 and Table A joins with Table C based on Col1, Col2 and Col3.
So if I do collect stats table A column (col1, col2, col3) is that enough to provide statistics details required for both queries (A join B and A join C)
or do I need to again collect stats based on Col1 and Col2 seperately besides collecting collectively on col1, col2 and col3.
How is the statstics information stored collectively on all the cols or seperately on the cols mentioned in the collect stats?
 
Thanks, Raam