根据执行计划优化sql语句

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。