【测试】使用hr用户下的employees表写一条SQL语句，执行计划走索引全扫描

SQL> select count(*) from employees;

  COUNT(*)
----------
       107


Execution Plan
----------------------------------------------------------
Plan hash value: 3580537945

-------------------------------------------------------------------------
| Id  | Operation        | Name         | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------------
|   0 | SELECT STATEMENT |              |     1 |     1   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE  |              |     1 |            |          |
|   2 |   INDEX FULL SCAN| EMP_EMAIL_UK |   107 |     1   (0)| 00:00:01 |
-------------------------------------------------------------------------


Statistics
----------------------------------------------------------
        224  recursive calls
          0  db block gets
        180  consistent gets
          1  physical reads
          0  redo size
        527  bytes sent via SQL*Net to client
        523  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          6  sorts (memory)
          0  sorts (disk)
          1  rows processed