使用_unnest_subquery优化sql

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标题:使用_unnest_subquery优化sql

作者:惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

一个复杂的sql查询,使用了大量EXISTS和NOT EXISTS 关联导致sql执行效率低下,这里挑选出来最核心的部分进行演示

SQL> explain plan for   select  
  2   a.aab034, a.aac001
  3    from si_dp.ac01_ac02 a
  4   where exists (select 1
  5            from ic40
  6           where aac001 = a.aac001
  7             and aae045 <= '201803'
  8             and aae120 = '0')
  9     and not exists (select 1
 10            from ic15
 11           where aac001 = a.aac001
 12             and aae002 <= '201803')
 13     and not EXISTS (select aab001
 14            from ab01
 15           where aab019 in ('91', '93')
 16             AND aab001 = a.aab001)
 17    and exists (select 1
 18            from ac13
 19           where aac001 = a.aac001
 20             and aae140 = '11'
 21             and aae114 in ('0', '1')
 22             and aae002 <= '201803')
 23     AND EXISTS (SELECT 1
 24            FROM AC13
 25           WHERE AAC001 = A.AAC001
 26             and aae140 = '11'
 27             AND AAE143 = '02'
 28             AND AAE003 < '201707'
 29             AND AAE002 BETWEEN '201801' AND '201803'
 30             and aae114 = '1')
 31     AND not EXISTS (SELECT 1
 32         FROM AC13
 33           WHERE AAC001 = A.AAC001
 34             and aae140 = '11'
 35          AND AAE002 < '201801')
 36     AND not EXISTS (SELECT 1
 37            FROM ac02
 38           WHERE AAC001 = A.AAC001
 39             and aae140 = '11'
 40             AND AAE036 < date '2018-1-1');
 
Explained.

Elapsed: 00:00:00.36

SQL> select * from table (dbms_xplan.display);


PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------
| Id  | Operation                         | Name               | Rows  | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |                    |     1 |   202 |       | 11172   (2)|
|   1 |  NESTED LOOPS SEMI                |                    |     1 |   202 |       | 11172   (2)|
|   2 |   NESTED LOOPS ANTI               |                    |     1 |   175 |       | 11168   (2)|
|   3 |    NESTED LOOPS SEMI              |                    |     1 |   150 |       | 11164   (2)|
|   4 |     NESTED LOOPS ANTI             |                    |     1 |   126 |       | 11160   (2)|
|   5 |      NESTED LOOPS SEMI            |                    |     1 |   104 |       | 11158   (2)|
|   6 |       NESTED LOOPS ANTI           |                    |     1 |    67 |       | 11145   (2)|
|   7 |        HASH JOIN ANTI             |                    |     1 |    50 |  8640K| 11143   (2)|
|   8 |         TABLE ACCESS FULL         | AC01_AC02          |   245K|  5755K|       |   356   (2)|
|   9 |         TABLE ACCESS FULL         | AC02               |   559K|    13M|       |  9346   (2)|
|  10 |        TABLE ACCESS BY INDEX ROWID| AB01               |     2 |    34 |       |     2   (0)|
|  11 |         INDEX UNIQUE SCAN         | PK_AB01            |     1 |       |       |     1   (0)|
|  12 |       TABLE ACCESS BY INDEX ROWID | AC13               |   325K|    11M|       |    13   (0)|
|  13 |        INDEX RANGE SCAN           | I_AC13_AAE143      |   446 |       |       |     4   (0)|
|  14 |      INDEX RANGE SCAN             | PK_IC15            |  1771K|    37M|       |     2   (0)|
|  15 |     TABLE ACCESS BY INDEX ROWID   | IC40               |    17M|   395M|       |     4   (0)|
|  16 |      INDEX RANGE SCAN             | PK_IC40            |     1 |       |       |     3   (0)|
|  17 |    TABLE ACCESS BY INDEX ROWID    | AC13               |    51M|  1236M|       |     4   (0)|
|  18 |     INDEX RANGE SCAN              | RELATION_233112_FK |     3 |       |       |     3   (0)|
|  19 |   TABLE ACCESS BY INDEX ROWID     | AC13               |    52M|  1350M|       |     4   (0)|
|  20 |    INDEX RANGE SCAN               | RELATION_233112_FK |     3 |       |       |     3   (0)|
-----------------------------------------------------------------------------------------------------

这条sql,在一个10.2.0.3的系统中执行了十几个小时无法出结果,开发商反馈,该大部分客户的11.2的环境中,大概十几分钟出结果.从来没有遇到此类情况.让我们给他优化sql.看到这个sql,第一反应就是很可能大量的NESTED LOOPS效率低下,怀疑统计信息错误,结果收集完统计信息之后,执行计划依旧,我就在思考怎么调整sql,让其不这样大量嵌套执行.想起来的_unnest_subquery是控制子查询嵌套转换的,从9i开始默认为true,尝试设置为false测试.

SQL> alter session set "_unnest_subquery"=false;

Session altered.

Elapsed: 00:00:00.00
SQL> explain plan for   select 
  2   a.aab034, a.aac001
  3    from si_dp.ac01_ac02 a
  4   where exists (select 1
  5            from ic40
  6           where aac001 = a.aac001
  7             and aae045 <= '201803'
  8             and aae120 = '0')
  9     and not exists (select 1
 10            from ic15
 11           where aac001 = a.aac001
 12             and aae002 <= '201803')
 13     and not EXISTS (select aab001
 14            from ab01
 15           where aab019 in ('91', '93')
 16             AND aab001 = a.aab001)
 17    and exists (select 1
 18            from ac13
 19          where aac001 = a.aac001
 20             and aae140 = '11'
 21             and aae114 in ('0', '1')
 22             and aae002 <= '201803')
 23     AND EXISTS (SELECT 1
 24            FROM AC13
 25           WHERE AAC001 = A.AAC001
 26             and aae140 = '11'
 27             AND AAE143 = '02'
 28             AND AAE003 < '201707'
 29             AND AAE002 BETWEEN '201801' AND '201803'
 30             and aae114 = '1')
 31     AND not EXISTS (SELECT 1
 32            FROM AC13
 33           WHERE AAC001 = A.AAC001
 34             and aae140 = '11'
 35             AND AAE002 < '201801')
 36     AND not EXISTS (SELECT 1
 37            FROM ac02
 38           WHERE AAC001 = A.AAC001
 39             and aae140 = '11'
 40             AND AAE036 < date '2018-1-1');
Explained.

Elapsed: 00:00:00.07

SQL> select * from table (dbms_xplan.display);


PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------
| Id  | Operation                     | Name             | Rows  | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                  |   185K|    19M|       |  2991K  (2)|
|   1 |  FILTER                       |                  |       |       |       |            |
|   2 |   HASH JOIN RIGHT SEMI        |                  |   185K|    19M|    16M|   758K  (3)|
|   3 |    TABLE ACCESS BY INDEX ROWID| AC13             |   353K|    12M|       |  4556   (1)|
|   4 |     INDEX SKIP SCAN           | I_AC13_AAB001    | 23608 |       |       |  2287   (1)|
|   5 |    HASH JOIN SEMI             |                  |   201K|    14M|    11M|   751K  (3)|
|   6 |     HASH JOIN SEMI            |                  |   201K|  9452K|  8640K|   123K  (3)|
|   7 |      TABLE ACCESS FULL        | AC01_AC02        |   245K|  5755K|       |   357   (2)|
|   8 |      TABLE ACCESS FULL        | IC40             |    21M|   481M|       | 86122   (3)|
|   9 |     TABLE ACCESS FULL         | AC13             |    52M|  1350M|       |   530K  (3)|
|  10 |   INDEX RANGE SCAN            | PK_IC15          |     2 |    44 |       |     3   (0)|
|  11 |   VIEW                        | index$_join$_009 |     1 |    17 |       |     3  (34)|
|  12 |    HASH JOIN                  |                  |       |       |       |            |
|  13 |     INDEX RANGE SCAN          | PK_AB01          |     1 |    17 |       |     2   (0)|
|  14 |     INLIST ITERATOR           |                  |       |       |       |            |
|  15 |      INDEX RANGE SCAN         | IDX_AB01_AAB019  |     1 |    17 |       |     8   (0)|
|  16 |   TABLE ACCESS BY INDEX ROWID | AC13             |     2 |    50 |       |     5   (0)|
|  17 |    INDEX RANGE SCAN           | I_AC13_SEARCH    |   152 |       |       |     4   (0)|
|  18 |   TABLE ACCESS BY INDEX ROWID | AC02             |     1 |    26 |       |     4   (0)|
|  19 |    INDEX RANGE SCAN           | PK_AC02          |     1 |       |       |     3   (0)|
-----------------------------------------------------------------------------------------------

让开发设置该参数,然后执行sql,结果3分钟不到出结果,非常圆满完成任务.该sql还有进一步优化空间,但是考虑到已经满足要求,不再折腾.

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