Question

I’m Working with a new Oracle DB, with one table having the following indexes:

• Index 1: ColA, ColB
• Index 2: ColA

Is the second index redundant, and Will this have a negative impact on performance?

Answer 1

Google is my best friend :

http://www.orafaq.com/node/926

The main point of this article is :

If 2 indexes ( I1 and I2 ) exist for a table and
   the number of columns in Index I1 is less or equal to the number of column in index I2 and
   index I1 has the same columns in the same order as leading columns of index I2 
Then
   If index I1 is UNIQUE then
      If index I2 is used to support Foregh Key or for Index Overload then
         Do Nothing
      Else
         Index I2 can be DROPPED
      End If
   Else
      Index I1 can be DROPPED
   End If
End If

And I’m agree with that !
In fact, search “duplicate indexes” in Google to have different kind of answer.