优化前：表连接使用merge
SQL> alter session set statistics_level=all;
Session altered.
SQL> select e.sal,d.dname from (select deptno,sum(sal) sal from emp group by deptno) e,dept d where d.deptno=e.deptno;
SAL DNAME
---------- --------------
8750 ACCOUNTING
10875 RESEARCH
9400 SALES
SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats +alias +outline'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID g2kzsydh3kmmq, child number 0
-------------------------------------
select e.sal,d.dname from (select deptno,sum(sal) sal from emp group by deptno) e,dept d where d.deptno=e.deptno
Plan hash value: 2992795152
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | O/1/M |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | | 6 |00:00:00.01 | 20 | | | |
| 1 | MERGE JOIN | | 2 | 3 | 6 |00:00:00.01 | 20 | | | |
| 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 2 | 4 | 8 |00:00:00.01 | 8 | | | |
| 3 | INDEX FULL SCAN | PK_DEPT | 2 | 4 | 8 |00:00:00.01 | 4 | | | |
|* 4 | SORT JOIN | | 8 | 3 | 6 |00:00:00.01 | 12 | 2048 | 2048 | 2/0/0|
| 5 | VIEW | | 2 | 3 | 6 |00:00:00.01 | 12 | | | |
| 6 | HASH GROUP BY | | 2 | 3 | 6 |00:00:00.01 | 12 | 1214K| 1214K| 2/0/0|
| 7 | TABLE ACCESS FULL | EMP | 2 | 14 | 28 |00:00:00.01 | 12 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / D@SEL$1
3 - SEL$1 / D@SEL$1
5 - SEL$2 / E@SEL$1
6 - SEL$2
7 - SEL$2 / EMP@SEL$2
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
DB_VERSION('11.2.0.4')
ALL_ROWS
OUTLINE_LEAF(@"SEL$2")
OUTLINE_LEAF(@"SEL$1")
INDEX(@"SEL$1" "D"@"SEL$1" ("DEPT"."DEPTNO"))
NO_ACCESS(@"SEL$1" "E"@"SEL$1")
LEADING(@"SEL$1" "D"@"SEL$1" "E"@"SEL$1")
USE_MERGE(@"SEL$1" "E"@"SEL$1")
FULL(@"SEL$2" "EMP"@"SEL$2")
USE_HASH_AGGREGATION(@"SEL$2")
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("D"."DEPTNO"="E"."DEPTNO")
filter("D"."DEPTNO"="E"."DEPTNO")
56 rows selected.
SQL>
将上面的执行计划中的merge改为hash连接，使用hint再次执行：
SQL> select /*+
2 BEGIN_OUTLINE_DATA
3 IGNORE_OPTIM_EMBEDDED_HINTS
4 OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
5 DB_VERSION('11.2.0.4')
6 ALL_ROWS
7 OUTLINE_LEAF(@"SEL$2")
8 OUTLINE_LEAF(@"SEL$1")
9 INDEX(@"SEL$1" "D"@"SEL$1" ("DEPT"."DEPTNO"))
10 NO_ACCESS(@"SEL$1" "E"@"SEL$1")
11 LEADING(@"SEL$1" "D"@"SEL$1" "E"@"SEL$1")
12 USE_HASH(@"SEL$1" "E"@"SEL$1")
13 FULL(@"SEL$2" "EMP"@"SEL$2")
14 USE_HASH_AGGREGATION(@"SEL$2")
15 END_OUTLINE_DATA
16 */ e.sal,d.dname from (select deptno,sum(sal) sal from emp group by deptno) e,dept d where d.deptno=e.deptno; SAL DNAME
---------- --------------
9400 SALES
10875 RESEARCH
8750 ACCOUNTING SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats +alias +outline')); PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID 5sns096pbcwj8, child number 0
-------------------------------------
select /*+ BEGIN_OUTLINE_DATA IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
DB_VERSION('11.2.0.4') ALL_ROWS OUTLINE_LEAF(@"SEL$2")
OUTLINE_LEAF(@"SEL$1") INDEX(@"SEL$1" "D"@"SEL$1"
("DEPT"."DEPTNO")) NO_ACCESS(@"SEL$1" "E"@"SEL$1")
LEADING(@"SEL$1" "D"@"SEL$1" "E"@"SEL$1") USE_HASH(@"SEL$1"
"E"@"SEL$1") FULL(@"SEL$2" "EMP"@"SEL$2")
USE_HASH_AGGREGATION(@"SEL$2") END_OUTLINE_DATA */
e.sal,d.dname from (select deptno,sum(sal) sal from emp group by
deptno) e,dept d where d.deptno=e.deptno Plan hash value: 208030399 -----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | O/1/M |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 3 |00:00:00.01 | 8 | | | |
|* 1 | HASH JOIN | | 1 | 3 | 3 |00:00:00.01 | 8 | 1599K| 1599K| 1/0/0|
| 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 4 | 4 |00:00:00.01 | 2 | | | |
| 3 | INDEX FULL SCAN | PK_DEPT | 1 | 4 | 4 |00:00:00.01 | 1 | | | |
| 4 | VIEW | | 1 | 3 | 3 |00:00:00.01 | 6 | | | |
| 5 | HASH GROUP BY | | 1 | 3 | 3 |00:00:00.01 | 6 | 1214K| 1214K| 1/0/0|
| 6 | TABLE ACCESS FULL | EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
----------------------------------------------------------------------------------------------------------------------------- Query Block Name / Object Alias (identified by operation id):
------------------------------------------------------------- 1 - SEL$1
2 - SEL$1 / D@SEL$1
3 - SEL$1 / D@SEL$1
4 - SEL$2 / E@SEL$1
5 - SEL$2
6 - SEL$2 / EMP@SEL$2 Outline Data
------------- /*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
DB_VERSION('11.2.0.4')
ALL_ROWS
OUTLINE_LEAF(@"SEL$2")
OUTLINE_LEAF(@"SEL$1")
INDEX(@"SEL$1" "D"@"SEL$1" ("DEPT"."DEPTNO"))
NO_ACCESS(@"SEL$1" "E"@"SEL$1")
LEADING(@"SEL$1" "D"@"SEL$1" "E"@"SEL$1")
USE_HASH(@"SEL$1" "E"@"SEL$1")
FULL(@"SEL$2" "EMP"@"SEL$2")
USE_HASH_AGGREGATION(@"SEL$2")
END_OUTLINE_DATA
*/ Predicate Information (identified by operation id):
--------------------------------------------------- 1 - access("D"."DEPTNO"="E"."DEPTNO") 62 rows selected. SQL>
针对该sql，在创建新的profile。