执行计划

Posted 2020-06-13

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了执行计划相关的知识，希望对你有一定的参考价值。

1. 预执行 explain plan for

实际并没有执行SQL语句。

SQL> explain plan for select ca_cstid from c_acc;

Explained.

SQL> @?/rdbms/admin/utlxpls

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

-----------------------------------------------------------------------------
| Id | Operation     | Name     | Rows | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |      1 |      7 |      1   (0)| 00:00:01 |
|   1 | INDEX FULL SCAN | DEPT_ACC |      1 |      7 |      1   (0)| 00:00:01 |
-----------------------------------------------------------------------------

8 rows selected.

SQL> @?/rdbms/admin/utlxplp

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

8 rows selected.

SQL> select plan_table_output from table(DBMS_XPLAN.DISPLAY());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3827578295

8 rows selected.

2. 即时执行计划

在执行SQL的同时查看执行计划。

SQL> set autotrace traceonly; # 运行查询但不显示查询结果；显示执行计划与统计信息
SQL> select ca_cstid from c_acc;

Execution Plan
----------------------------------------------------------
Plan hash value: 3827578295

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

SQL>

SQL> set autotrace traceonly explain #不运行查询（DML操作会运行）；显示执行计划，不显示统计信息。
SQL> select ca_cstid from c_acc;

Execution Plan
----------------------------------------------------------
Plan hash value: 3827578295

SQL>

3. 查看指定SQL执行计划

查看已经执行过的SQL的执行计划

查看v$sql_plan中最后一个会话SQL的执行计划

SQL> set linesize 160
SQL> select plan_table_output from table(dbms_xplan.display_cursor());

Execution Plan
----------------------------------------------------------
Plan hash value: 3713220770

----------------------------------------------------------------------------------------------------
| Id | Operation              | Name       | Rows | Bytes | Cost (%CPU)| Time       |
----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT          |           | 8168 | 16336 |    29   (0)| 00:00:01 |
|   1 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY_CURSOR | 8168 | 16336 |    29   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------

通过SQL_ID查询其执行计划

SQL> set autotrace traceonly

SQL> select mb_id,mb_tname from mng_bak;

2294 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 1749878440

-----------------------------------------------------------------------------
| Id | Operation      | Name    | Rows | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        | 2294 | 59644 |     12   (0)| 00:00:01 |
|   1 | TABLE ACCESS FULL| MNG_BAK | 2294 | 59644 |     12   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Statistics
----------------------------------------------------------
      0 recursive calls
      0 db block gets
    188 consistent gets
      0 physical reads
      0 redo size
      90151 bytes sent via SQL*Net to client
       2191 bytes received via SQL*Net from client
    154 SQL*Net roundtrips to/from client
      0 sorts (memory)
      0 sorts (disk)
       2294 rows processed

SQL>

SQL> set autotrace off
SQL> select sql_id,child_number from v$sql where sql_text like ‘select mb_id,mb_tname from mng_bak%‘;

SQL_ID CHILD_NUMBER
------------- ------------
bk8rtgsb6jm37 0

SQL>

SQL> set linesize 80
SQL> select plan_table_output from table(dbms_xplan.display_cursor(‘bk8rtgsb6jm37‘,0,‘TYPICAL‘));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID bk8rtgsb6jm37, child number 0
-------------------------------------
select mb_id,mb_tname from mng_bak

Plan hash value: 1749878440

-----------------------------------------------------------------------------
| Id | Operation      | Name    | Rows | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |        |        |     12 (100)|        |
|   1 | TABLE ACCESS FULL| MNG_BAK | 2294 | 59644 |     12   (0)| 00:00:01 |

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

13 rows selected.

4. 历史执行计划 dba_hist_sql_plan

dba_hist_sql_plan 与 dba_hist_sqltext 通过SQL_ID关联。

SQL> desc dba_hist_sqltext
Name                       Null?    Type
----------------------------------------- -------- ----------------------------
DBID                       NOT NULL NUMBER
SQL_ID                    NOT NULL VARCHAR2(13)
SQL_TEXT                        CLOB
COMMAND_TYPE                        NUMBER

SQL> select p.* from dba_hist_sqltext t,table(DBMS_XPLAN.DISPLAY_AWR(t.sql_id,null,null,‘TYPICAL‘)) p where t.sql_text like ‘select mb_id,mb_tname from mng_bak%‘;

no rows selected

以上是关于执行计划的主要内容，如果未能解决你的问题，请参考以下文章

C++ 代码片段执行

执行代码时有时不显示对话框片段

选项卡执行android中下一个片段中存在的代码

Sleep() 方法后的代码片段没有被执行

当活动被破坏但我必须继续执行片段中的代码时该怎么办？

当 ViewPager 中的片段出现和消失时如何执行一些代码