Oracle 12C 同列多索引

在Oracle 12c中，Oracle提供了可以在同一个表的列上建立不同的索引，用来做SQL的性能优化，但是仅有一个索引是可见的。

下面是一个示例
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SQL>  alter session set container=pdb1;

Session altered.

SQL> CREATE TABLE t (
  2  id            NUMBER,
  3    ename  VARCHAR2(50)
  4  );

Table created.

SQL> CREATE INDEX t_idx1 ON t(ename) VISIBLE;

Index created.

SQL> CREATE INDEX t_idx2 ON t(ename) INVISIBLE;
CREATE INDEX t_idx2 ON t(ename) INVISIBLE
                        *
ERROR at line 1:
ORA-01408: such column list already indexed

SQL> CREATE BITMAP INDEX t_idx3 ON t(ename) INVISIBLE;

Index created.
SQL> l
  1  SELECT a.index_name,
  2        a.index_type,
  3        a.partitioned,
  4        b.partitioning_type,
  5        b.locality,
  6        a.visibility
  7  FROM  user_indexes a
  8        LEFT OUTER JOIN user_part_indexes b ON a.index_name = b.index_name where a.table_name='T'
  9* ORDER BY index_name
SQL> /

INDEX_NAME INDEX_TYPE PARTITIONED  PARTITIONING_TYPE          LOCALITY VISIBILITY
---------- ---------- ------------ --------------------------- -------- ----------
T_IDX1    NORMAL    NO                                                VISIBLE
T_IDX3    BITMAP    NO                                                INVISIBLE