oracle 提供了最佳化建議功能包DBMS_SQLTUNE，該包可以幫助我們分析SQL，並提供最佳化建議。

原有執行計劃
alter session set statistics_level=all;
set serveroutput off
select * from test.emp where ename='SCOTT' and DEPTNO=20;
SELECT * FROM table(dbms_xplan.display_cursor(NULL,NULL,'runstats_last'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------
SQL_ID 8k1gbrapm7zpd, child number 0
-------------------------------------
select * from test.emp where ename='SCOTT' and DEPTNO=20

Plan hash value: 3956160932

------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 4 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 1 | 1 |00:00:00.01 | 4 |
-------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("ENAME"='SCOTT' AND "DEPTNO"=20))

下面就用DBMS_SQLTUNE最佳化該SQL
--1.賦予使用者ADVISOR許可權
grant ADVISOR to test;

--2.建立sql tuning任務
conn test/test

DECLARE
my_task_name VARCHAR2(30);
my_sqltext CLOB;
BEGIN
my_sqltext := 'select * from emp where ename= :name and DEPTNO= :deptno';
my_task_name := DBMS_SQLTUNE.CREATE_TUNING_TASK(
sql_text => my_sqltext,
bind_list => sql_binds(anydata.convertvarchar2(10),anydata.convertnumber(2)),
user_name => 'TEST',
scope => 'COMPREHENSIVE',
time_limit => 60,
task_name => 'test_sql_tuning',
description => 'Task to tune a query on emp');
END;
/

引數說明：
bind_list：多個繫結變數以','逗號分隔。引數值一定要根據繫結變數對應的列的型別書寫.
如：emp.ename型別是VARCHAR2(10)，那麼就要寫成
bind_list =>sql_binds(anydata.convertvarchar2(10)),

time_limit：執行的最長時間，預設是60。

scope：
LIMITED，用大概1秒時間去最佳化SQL語句，但是並不進行SQL Profiling分析。
COMPREHENSIVE，進行全面分析，包含SQL Profiling分析；比LIMITED用時更長。

/*2014-4-8日增加 begin */
**也可以用sql_id建立sql tunning任務，比用sql_text方便很多
FUNCTION CREATE_TUNING_TASK RETURNS VARCHAR2
Argument Name Type In/Out Default?
------------------------------ ----------------------- ------ --------
SQL_ID VARCHAR2 IN
PLAN_HASH_VALUE NUMBER IN DEFAULT
SCOPE VARCHAR2 IN DEFAULT
TIME_LIMIT NUMBER IN DEFAULT
TASK_NAME VARCHAR2 IN DEFAULT
DESCRIPTION VARCHAR2 IN DEFAULT

DECLARE
my_task_name VARCHAR2(30);
BEGIN
my_task_name := DBMS_SQLTUNE.CREATE_TUNING_TASK(
SQL_ID => 'ddw7j6yfnw0vz',
scope => 'COMPREHENSIVE',
time_limit => 60,
task_name => 'tunning_task_ddw7j6yfnw0vz',
description => 'Task to tune a query on ddw7j6yfnw0vz');
END;
/

/*2014-4-8日增加 end */

--3.檢視任務名 SELECT TASK_NAME
FROM DBA_ADVISOR_LOG
WHERE OWNER = 'TEST';
TASK_NAME
------------------------------
test_sql_tuning

--4.執行sql tuning任務
BEGIN
DBMS_SQLTUNE.EXECUTE_TUNING_TASK( task_name => 'test_sql_tuning' );
END;
/

--5.檢視sql tunning任務狀態
SELECT status
FROM USER_ADVISOR_TASKS
WHERE task_name = 'test_sql_tuning';
STATUS
-----------
COMPLETED

--6.展示sql tunning結果
SET LONG 10000
SET LONGCHUNKSIZE 1000
SET LINESIZE 100
SELECT DBMS_SQLTUNE.REPORT_TUNING_TASK('test_sql_tuning')
FROM DUAL;

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : test_sql_tuning
Tuning Task Owner : TEST
Workload Type : Single SQL Statement
Scope : COMPREHENSIVE
Time Limit(seconds): 60
Completion Status : COMPLETED
Started at : 04/01/2014 16:45:16
Completed at : 04/01/2014 16:45:17

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Schema Name: TEST
SQL ID : 95fv6dbj64d0f
SQL Text : select * from emp where ename= :name and DEPTNO= :deptno

-------------------------------------------------------------------------------
FINDINGS SECTION (2 findings)
-------------------------------------------------------------------------------
1- Statistics Finding
---------------------

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
Table "TEST"."EMP" was not analyzed.

Recommendation
--------------
- Consider collecting optimizer statistics for this table.
execute dbms_stats.gather_table_stats(ownname => 'TEST', tabname =>
'EMP', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,
method_opt => 'FOR ALL COLUMNS SIZE AUTO');

Rationale
---------

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
The optimizer requires up-to-date statistics for the table in order to
select a good execution plan.

2- Index Finding (see explain plans section below)
--------------------------------------------------
The execution plan of this statement can be improved by creating one or more
indices.

Recommendation (estimated benefit: 66.67%)
------------------------------------------
- Consider running the Access Advisor to improve the physical schema design

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
or creating the recommended index.
create index TEST.IDX$$_00D80001 on TEST.EMP("ENAME","DEPTNO");

Rationale
---------
Creating the recommended indices significantly improves the execution plan
of this statement. However, it might be preferable to run "Access Advisor"
using a representative SQL workload as opposed to a single statement. This
will allow to get comprehensive index recommendations which takes into
account index maintenance overhead and additional space consumption.

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------

1- Original
-----------
Plan hash value: 3956160932

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 87 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 87 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("ENAME"=:NAME AND "DEPTNO"=:DEPTNO)

2- Using New Indices
--------------------

DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
Plan hash value: 2106247215
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 87 | 1 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 87 | 1 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX$$_00D80001 | 1 | | 1 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
DBMS_SQLTUNE.REPORT_TUNING_TASK('TEST_SQL_TUNING')
----------------------------------------------------------------------------------------------------
---------------------------------------------------
2 - access("ENAME"=:NAME AND "DEPTNO"=:DEPTNO)

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

建議報告總結：
<1>收集EMP表的統計資訊
execute dbms_stats.gather_table_stats(ownname => 'TEST', tabname =>'EMP', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,method_opt => 'FOR ALL COLUMNS SIZE AUTO');

<2>建立索引
create index TEST.IDX$$_00D80001 on TEST.EMP("ENAME","DEPTNO");

最佳化後執行計劃
--------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 3 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 3 |
|* 2 | INDEX RANGE SCAN | IDX$$_00D80001 | 1 | 1 | 1 |00:00:00.01 | 2 |
--------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ENAME"='SCOTT' AND "DEPTNO"=20)

--7.完成後刪除sql tunning任務
EXEC DBMS_SQLTUNE.DROP_TUNING_TASK('test_sql_tuning');

--8.其他
--sql tunning任務建立後，也可以修改引數
BEGIN
DBMS_SQLTUNE.SET_TUNING_TASK_PARAMETER(
task_name => 'test_sql_tuning',
parameter => 'TIME_LIMIT', value => 300);
END;
/

--檢視SQL Tuning Advisor的進展（task執行很久）
col opname for a20
col ADVISOR_NAME for a20
SELECT SID,SERIAL#,USERNAME,OPNAME,ADVISOR_NAME,TARGET_DESC,START_TIME SOFAR, TOTALWORK
FROM V$ADVISOR_PROGRESS
WHERE USERNAME = 'TEST';

以上根據oracle doc整理

SQL調優工具包DBMS_SQLTUNE的使用方法

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