Composite Secondary Index- - response (2) by Nishant.Bhardwaj

thanks Jeff for the quick reply..
In case the col_a and col_b are highly selective then do we go for composite index on (col_A,co_b)?
also why do we call it a covered query? are there are some scenrios in which even if we create SI's then the
query is not covered ? can you please elaborate more on this..
 
thanks!
cheers!
Nishant