Invisible Index

To create an invisible index: 

Use the CREATE INDEX statement with the INVISIBLE keyword.

Example:

The following statement creates an invisible index named ename_index for the ename column of the emp table:

CREATE INDEX emp_index ON emp(ename)
      TABLESPACE empdata
      STORAGE (INITIAL 20K NEXT 20k)
      INVISIBLE;

 

 An invisible index is an index that is ignored by the optimizer.

     You have to explicitly set the initialization parameter OPTIMIZER_USE_INVISIBLE_INDEXES  =  TRUE at the session or system level.