DBMS_XPLAN是Oracle提供的一个用于查看SQL计划，包括执行计划和解释计划的包；在以前查看SQL执行计划的时候，我都是使用set autotrace命令，不过现在看来，DBMS_XPLAN包给出了更加简化的获取和显示计划的方式。
这5个函数分别对应不同的显示计划的方式，DBMS_XPLAN包不仅可以获取解释计划，它还可以用来输出存储在AWR，SQL调试集，缓存的SQL游标，以及SQL基线中的语句计划，实现如上的功能，通常会用到一下5个方法：
1.DISPLAY
2.DISPLAY_AWR
3.DISPLAY_CURSOR
4.DISPLAY_PLAN
5.DISPLAY_SQL_PLAN_BASELINE
6.DISPLAY_SQLSET
下面将重点讨论关于DBMS_XPLAN包在解释计划和执行计划上的应用。
来看一个经常使用的查看某条语句的解释计划示例：
Predicate Information (identified by operation id):
3 - filter("E"."ENAME"='JONES')
4 - access("E"."DEPTNO"="D"."DEPTNO")
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
"E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
"E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
"D"."DEPTNO"[NUMBER,22], "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]
2 - (#keys=0) "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10],
"E"."JOB"[VARCHAR2,9], "E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7],
"E"."SAL"[NUMBER,22], "E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22],
"D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
3 - "E"."EMPNO"[NUMBER,22], "E"."ENAME"[VARCHAR2,10], "E"."JOB"[VARCHAR2,9],
"E"."MGR"[NUMBER,22], "E"."HIREDATE"[DATE,7], "E"."SAL"[NUMBER,22],
"E"."COMM"[NUMBER,22], "E"."DEPTNO"[NUMBER,22]
4 - "D".ROWID[ROWID,10], "D"."DEPTNO"[NUMBER,22]
5 - "D"."DNAME"[VARCHAR2,14], "D"."LOC"[VARCHAR2,13]
43 rows selected.
-- 去除执行计划上的字节数和成本统计信息
SQL> select empno, ename from emp e, dept d
2 where e.deptno = d.deptno
3 and e.ename = 'JONES' ;
EMPNO ENAME
---------- ----------
7566 JONES
SQL> select * from table(dbms_xplan.display_cursor(null,null,format=>'ALLSTATS LAST -COST -BYTES'));
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID 3mypf7d6npa97, child number 1
-------------------------------------
select empno, ename from emp e, dept d where e.deptno = d.deptno and
e.ename = 'JONES'
Plan hash value: 3956160932
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 8 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 1 | 1 |00:00:00.01 | 8 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("E"."ENAME"='JONES' AND "E"."DEPTNO" IS NOT NULL))
19 rows selected.
-- 另一种选项，窥视绑定变量的值，非常方便！！
SQL> variable v_empno number
SQL> exec :v_empno := 7566 ;
PL/SQL procedure successfully completed.
SQL> select * from emp where empno = :v_empno ;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7566 JONES MANAGER 7839 02-APR-81 2975 20
SQL> select * from table(dbms_xplan.display_cursor(null,null,format=>'+PEEKED_BINDS'));
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID 9q17w9umt58m7, child number 0
-------------------------------------
select * from emp where empno = :v_empno
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 38 | 1 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| |
--------------------------------------------------------------------------------------
Peeked Binds (identified by position):
--------------------------------------
1 - :V_EMPNO (NUMBER): 7566
Predicate Information (identified by operation id):
---------------------------------------------------
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
2 - access("EMPNO"=:V_EMPNO)
24 rows selected.
-- 并行查询信息筛选
SQL> select /*+ parallel(d, 4) parallel (e, 4) */
2 d.dname, avg(e.sal), max(e.sal)
3 from dept d, emp e
4 where d.deptno = e.deptno
5 group by d.dname
6 order by max(e.sal), avg(e.sal) desc;
DNAME AVG(E.SAL) MAX(E.SAL)
-------------- ---------- ----------
SALES 1566.66667 2850
RESEARCH 2175 3000
ACCOUNTING 2916.66667 5000
SQL> select * from table(dbms_xplan.display_cursor(null,null,'TYPICAL -BYTES -COST'));
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
SQL_ID gahr597f78j0d, child number 0
-------------------------------------
select /*+ parallel(d, 4) parallel (e, 4) */ d.dname, avg(e.sal),
max(e.sal) from dept d, emp e where d.deptno = e.deptno group by
d.dname order by max(e.sal), avg(e.sal) desc
Plan hash value: 3078011448
--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Time | TQ |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------------------------------
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | | | |
| 1 | PX COORDINATOR | | | | | | |
| 2 | PX SEND QC (ORDER) | :TQ10004 | 4 | 00:00:01 | Q1,04 | P->S | QC (ORDER) |
| 3 | SORT ORDER BY | | 4 | 00:00:01 | Q1,04 | PCWP | |
| 4 | PX RECEIVE | | 4 | 00:00:01 | Q1,04 | PCWP | |
| 5 | PX SEND RANGE | :TQ10003 | 4 | 00:00:01 | Q1,03 | P->P | RANGE |
| 6 | HASH GROUP BY | | 4 | 00:00:01 | Q1,03 | PCWP | |
| 7 | PX RECEIVE | | 14 | 00:00:01 | Q1,03 | PCWP | |
| 8 | PX SEND HASH | :TQ10002 | 14 | 00:00:01 | Q1,02 | P->P | HASH |
|* 9 | HASH JOIN BUFFERED | | 14 | 00:00:01 | Q1,02 | PCWP | |
| 10 | PX RECEIVE | | 4 | 00:00:01 | Q1,02 | PCWP | |
| 11 | PX SEND HASH | :TQ10000 | 4 | 00:00:01 | Q1,00 | P->P | HASH |
| 12 | PX BLOCK ITERATOR | | 4 | 00:00:01 | Q1,00 | PCWC | |
|* 13 | TABLE ACCESS FULL| DEPT | 4 | 00:00:01 | Q1,00 | PCWP | |
| 14 | PX RECEIVE | | 14 | 00:00:01 | Q1,02 | PCWP | |
| 15 | PX SEND HASH | :TQ10001 | 14 | 00:00:01 | Q1,01 | P->P | HASH |
| 16 | PX BLOCK ITERATOR | | 14 | 00:00:01 | Q1,01 | PCWC | |
|* 17 | TABLE ACCESS FULL| EMP | 14 | 00:00:01 | Q1,01 | PCWP | |
--------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
9 - access("D"."DEPTNO"="E"."DEPTNO")
13 - access(:Z>=:Z AND :Z<=:Z) 17 - access(:Z>=:Z AND :Z<=:Z)
38 rows selected.