具有多个相同列索引的Oracle性能

Question

我正在使用新的Oracle DB,其中一个表具有以下索引:

• 索引1:ColA,ColB
• 指数2:ColA

第二个索引是多余的,这会对性能产生负面影响吗？

Answer 1

谷歌是我最好的朋友:

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

本文的重点是:

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

我同意这一点!实际上,在Google中搜索"重复索引"会有不同类型的答案.