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标题: 使用 gather_plan_statistics hint 产生执行计划 [打印本页]

作者: 郑全 时间: 2017-1-17 18:27
标题: 使用 gather_plan_statistics hint 产生执行计划
、首先sqlplus登陆当前用户
2、执行  运行 sql语句，在语句中加入    /*+ gather_plan_statistics */
例子：执行  sql 语句  select /*+ gather_plan_statistics */  count(employee_id) from hr.employees where department_id=50;
得到结果  ：
COUNT(1)
----------
45
3、执行查看计划 select * from table(dbms_xplan.display_cursor(NULL,NULL,'ALLSTATS'));
得到结果：

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

SQL_ID  4dxpaqxz24a4q, child number 0
-------------------------------------
select /*+ gather_plan_statistics */  count(employee_id) from
hr.employees where department_id=50
Plan hash value: 2271004725
--------------------------------------------------------------------------------

| Id  | Operation       | Name             | Starts | E-Rows | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------

| 0 | SELECT STATEMENT  |                |    1 |       |    1 |00:00:00.01 |    1 | PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------------------------------------------------------------------
| 1 |  SORT AGGREGATE |                |    1 |    1 |    1 |00:00:00.01 |    1 |
|*  2 | INDEX RANGE SCAN| EMP_DEPARTMENT_IX |    1 |    45 |    45 |00:00:00.01 |    1 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("DEPARTMENT_ID"=50)

20 rows selected.
SQL>

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