EXPLAINPLANFOR和SETAUTOTRACE之間的差別是什么

本篇文章為大家展示了EXPLAIN PLAN FOR 和 SET AUTOTRACE之間的差別是什么，內(nèi)容簡(jiǎn)明扼要并且容易理解，絕對(duì)能使你眼前一亮，通過這篇文章的詳細(xì)介紹希望你能有所收獲。

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通常我們使用 EXPLAIN PLAN FOR 和 SET AUTOTRACE 來(lái)查看sql語(yǔ)句的執(zhí)行計(jì)劃，這里做一個(gè)小實(shí)驗(yàn)來(lái)看看兩種方法對(duì)sql執(zhí)行情況的差別。
yang@rac1>create table yang_t as select * from t;
Table created.
yang@rac1>set autot on exp
yang@rac1>select * from yang_t;
        ID NAME
---------- ------------------
    130864 YANG_SEQ
    132031 YANG_A
    132032 SYS_C0066382
    132033 YANG_B
    132034 SYS_C0066383
    132035 FACT
    132036 MLOG$_YANG_A
    132037 MLOG$_YANG_B
    132038 MLOG$_FACT
    132039 T
    131949 YANG_ROWID
    131951 YANG_PK
    131952 SYS_C0066303
    131955 YANG_OBJECT
    131956 YANG_OID
    131957 SYS_C0066304
    132018 YANG_C
    132017 MV_CAPABILITIES_TABLE
    132030 MLOG$_YANG_PK
    132027 MLOG$_YANG_ROWID
           LINKORACL
           LINKYANG
22 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2508602004
----------------------------------------------------------------------------
| Id | Operation         | Name   | Rows | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |    22 | 1738 |     3   (0)| 00:00:01 |
|   1 | TABLE ACCESS FULL| YANG_T |    22 | 1738 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement (level=2)

yang@rac1>set autot off
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'select * from yang_t';
EXECUTIONS PARSE_CALLS
---------- -----------
         1           1
yang@rac1>set autot on exp
yang@rac1>set autotrace traceonly
yang@rac1>select * from yang_t;
22 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2508602004
----------------------------------------------------------------------------
| Id | Operation         | Name   | Rows | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |    22 | 1738 |     3   (0)| 00:00:01 |
|   1 | TABLE ACCESS FULL| YANG_T |    22 | 1738 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------
Note
-----
   - dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
         21 recursive calls
         61 db block gets
         33 consistent gets
          6 physical reads
      14040 redo size
       1082 bytes sent via SQL*Net to client
        520 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
         22 rows processed
yang@rac1>set autot off
再次查詢是否執(zhí)行?？梢钥闯鍪褂胹et autotrace 查看執(zhí)行計(jì)劃時(shí)，oracle會(huì)執(zhí)行一下sql語(yǔ)句的。
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'select * from yang_t';
EXECUTIONS PARSE_CALLS
---------- -----------
         2           2
對(duì)測(cè)試表進(jìn)行dml操作。并查看dml 的執(zhí)行情況。
yang@rac1>insert into yang_t values (1,2);
1 row created.
yang@rac1>commit;
Commit complete.
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'insert into yang_t values (1,2);';
no rows selected
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'insert into yang_t values%';
EXECUTIONS PARSE_CALLS
---------- -----------
         1           1
=======EXPLAIN PLAN FOR ========
實(shí)驗(yàn)一下EXPLAIN PLAN 查看sql語(yǔ)句執(zhí)行計(jì)劃的情況。
yang@rac1>EXPLAIN PLAN FOR SELECT * FROM YANG_T;
Explained.
yang@rac1>SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------
Plan hash value: 2508602004
----------------------------------------------------------------------------
| Id | Operation         | Name   | Rows | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |    23 | 1817 |     4   (0)| 00:00:01 |
|   1 | TABLE ACCESS FULL| YANG_T |    23 | 1817 |     4   (0)| 00:00:01 |
----------------------------------------------------------------------------
Note
-----
   - dynamic sampling used for this statement (level=2)
12 rows selected.
從下面的查詢結(jié)果中可以看出使用EXPLAIN PLAN FOR 查看執(zhí)行計(jì)劃時(shí)oracle是沒有執(zhí)行要查看執(zhí)行計(jì)劃的sql 語(yǔ)句的。
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'SELECT * FROM YANG_T%';
no rows selected
yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'SELECT * FROM YANG%';

no rows selected

yang@rac1>select executions,parse_calls from v$sqlarea where sql_text like 'select * from yang_t';
EXECUTIONS PARSE_CALLS
---------- -----------
         2           2
yang@rac1>
小結(jié)：
     EXPLAIN PLAN FOR 方式查看執(zhí)行計(jì)劃時(shí)oracle本身并不真正的執(zhí)行該sql 語(yǔ)句，只是對(duì)sql進(jìn)行解析獲取執(zhí)行計(jì)劃。
SET AUTOTRACE   方式查看sql語(yǔ)句的執(zhí)行計(jì)劃則是oracle 則對(duì)sql進(jìn)行解析并執(zhí)行的。

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