在程序处理分页时，有时需要使用count(*)查询，而如果表很大的时候，用此方法无疑瓶颈所在，今天发现了一个解决办法就是如果这个表有唯一列的话(比如主键)，那我们可以使用主键，强制走索引来缩短查询时间。

主键：id

索引：SYS_C0029630

SQL> select /*+ index(tt SYS_C0029630) */count(id) from tt;

COUNT(ID)

----------

75651

Execution Plan

----------------------------------------------------------

Plan hash value: 3525147495

-------------------------------------------------------------------------

| Id  | Operation        | Name         | Rows  | Cost (%CPU)| Time     |

-------------------------------------------------------------------------

|   0 | SELECT STATEMENT |              |     1 |   213   (0)| 00:00:01 |

|   1 |  SORT AGGREGATE  |              |     1 |            |          |

|   2 |   INDEX FULL SCAN| SYS_C0029630 | 88573 |   213   (0)| 00:00:01 |

-------------------------------------------------------------------------

Note

-----

- dynamic sampling used for this statement (level=2)

Statistics

----------------------------------------------------------

4  recursive calls

0  db block gets

287  consistent gets

0  physical reads

0  redo size

425  bytes sent via SQL*Net to client

419  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

SQL> desc tt;

Name                                      Null?    Type

----------------------------------------- -------- ----------------------------

ID                                        NOT NULL NUMBER(38)

NAME                                               VARCHAR2(2)