Oracle New in 12c

This article gives the introduction to new features in Oracle Database 12c 

 Multiple Same Column Indexes
   Now you can create an index on the same column(s) on which there exist an Index.
   Mension INVISIBLE key word to do the same.
  
   Usage : In optimizer you can use them as
            > alter session set optimizer_use_invisible_indexes=true;
            > exec dbms_stats.set_table_stats ( user, 'TAB1', numrows => 1000000, numblks => 100000 );
            > set autotrace traceonly explain select count(*) from tab1;

          
 Temporal Validity
  > create table addresses
    ( empno       number,    addr_data   varchar2(30),    start_date  date,    end_date    date,
      period for valid(start_date,end_date)
    )
    insert some data with defferent start_date and end_dates
  > select * from addresses as of period for valid sysdate;
    This will give data where sysdate is between start_date and end_date;



 Invisible Columns
    Syntax: alter table tab1 add ( pin int INVISIBLE );
     This will not displayed when you say :
       desc tab1;
       select * from tab1; or even when you Insert .
    To revert : alter table tab1 modify pin visible;
    Usage : This helps adding a column in the middle.
   
  Partial Indexs
 
     We can create a partial indexes for some partitions of the table;
     Also we can create a partial local index for a global partition table;