春节回来上班第一天也够蛋疼的，盖儿又给我发了一个SQL，他说这个SQL db file sequential read 很高，要跑120秒，逻辑读有1626677 叫我帮忙优化一下，SQL语句如下：
select distinct decode(length(a.category_id),
5,
decode(a.origin_type, 801, 888888, 999999),
a.category_id) category_id,
a.notice_code,
a.treat_status,
lr.real_name as receiver_name,
f.send_code,
f.policy_code,
g.real_name agent_name,
f.organ_id,
f.dept_id,
a.policy_id,
a.change_id,
a.case_id,
a.group_policy_id,
a.fee_id,
a.auth_id,
a.pay_id,
cancel_appoint.appoint_time cancel_appoint_time,
a.insert_time,
a.send_time,
a.end_time,
f.agency_code,
a.REPLY_TIME,
a.REPLY_EMP_ID,
a.FIRST_DUTY,
a.NEED_SEND_PRINT,
11 source
from t_policy_problem a,
t_policy f,
t_agent g,
t_letter_receiver lr,
t_problem_category pc,
t_policy_cancel_appoint cancel_appoint
where f.agent_id = g.agent_id(+)
and a.policy_id = f.policy_id(+)
and lr.main_receiver = 'Y'
and a.category_id = pc.category_id
and a.item_id = lr.item_id
and a.policy_id = cancel_appoint.policy_id(+)
And a.Item_Id = (Select Max(item_id)
From t_Policy_Problem
Where notice_code = a.notice_code)
and a.policy_id is not null
and a.notice_code is not null
and a.change_id is null
and a.case_id is null
and a.group_policy_id is null
and a.origin_type not in (801, 802)
and a.pay_id is null
and a.category_id not in
(130103, 130104, 130102, 140102, 140101)
and f.policy_type = 1
and (a.fee_id is null or
(a.fee_id is not null and a.origin_type = 701))
and f.organ_id in
(select distinct organ_id
from T_COMPANY_ORGAN
start with organ_id = '107'
connect by parent_id = prior organ_id)
and pc.NEED_PRITN = 'Y'
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
--------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 242 | 731 (1)|
| 1 | SORT UNIQUE | | 1 | 242 | 729 (0)|
|* 2 | FILTER | | | | |
|* 3 | HASH JOIN | | 1 | 242 | 714 (1)|
| 4 | NESTED LOOPS | | 1 | 236 | 712 (1)|
| 5 | NESTED LOOPS OUTER | | 1 | 219 | 711 (1)|
| 6 | NESTED LOOPS | | 1 | 203 | 710 (1)|
| 7 | NESTED LOOPS | | 1 | 196 | 709 (1)|
| 8 | NESTED LOOPS OUTER | | 1 | 121 | 708 (1)|
|* 9 | TABLE ACCESS FULL | T_POLICY_PROBLEM | 1 | 107 | 706 (0)|
| 10 | TABLE ACCESS BY INDEX ROWID| T_POLICY_CANCEL_APPOINT | 1 | 14 | 2 (50)|
|* 11 | INDEX UNIQUE SCAN | UK1_POLICY_CANCEL_APPOINT | 1 | | |
|* 12 | TABLE ACCESS BY INDEX ROWID | T_POLICY | 1 | 75 | 2 (50)|
|* 13 | INDEX UNIQUE SCAN | PK_T_POLICY | 1 | | 1 (0)|
|* 14 | TABLE ACCESS BY INDEX ROWID | T_PROBLEM_CATEGORY | 1 | 7 | 2 (50)|
|* 15 | INDEX UNIQUE SCAN | PK_T_PROBLEM_CATEGORY | 1 | | |
| 16 | TABLE ACCESS BY INDEX ROWID | T_AGENT | 1 | 16 | 2 (50)|
|* 17 | INDEX UNIQUE SCAN | PK_T_AGENT | 1 | | |
|* 18 | INDEX RANGE SCAN | T_LETTER_RECEIVER_IDX_001 | 1 | 17 | 2 (0)|
| 19 | VIEW | VW_NSO_1 | 7 | 42 | |
|* 20 | CONNECT BY WITH FILTERING | | | | |
| 21 | NESTED LOOPS | | | | |
|* 22 | INDEX UNIQUE SCAN | PK_T_COMPANY_ORGAN | 1 | 6 | |
| 23 | TABLE ACCESS BY USER ROWID | T_COMPANY_ORGAN | | | |
| 24 | NESTED LOOPS | | | | |
| 25 | BUFFER SORT | | 7 | 70 | |
| 26 | CONNECT BY PUMP | | | | |
|* 27 | INDEX RANGE SCAN | T_COMPANY_ORGAN_IDX_002 | 7 | 70 | 1 (0)|
| 28 | SORT AGGREGATE | | 1 | 21 | |
| 29 | TABLE ACCESS BY INDEX ROWID | T_POLICY_PROBLEM | 1 | 21 | 2 (50)|
|* 30 | INDEX RANGE SCAN | IDX_POLICY_PROBLEM__N_CODE | 1 | | 3 (0)|
--------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("SYS_ALIAS_1"."ITEM_ID"= (SELECT /*+ */ MAX("T_POLICY_PROBLEM"."ITEM_ID") FROM
"T_POLICY_PROBLEM" "T_POLICY_PROBLEM" WHERE "T_POLICY_PROBLEM"."NOTICE_CODE"=:B1))
3 - access("F"."ORGAN_ID"="VW_NSO_1"."$nso_col_1")
9 - filter("SYS_ALIAS_1"."POLICY_ID" IS NOT NULL AND "SYS_ALIAS_1"."NOTICE_CODE" IS NOT NULL AND
"SYS_ALIAS_1"."CHANGE_ID" IS NULL AND "SYS_ALIAS_1"."CASE_ID" IS NULL AND
"SYS_ALIAS_1"."GROUP_POLICY_ID" IS NULL AND TO_NUMBER("SYS_ALIAS_1"."ORIGIN_TYPE")<>801 AND
TO_NUMBER("SYS_ALIAS_1"."ORIGIN_TYPE")<>802 AND "SYS_ALIAS_1"."PAY_ID" IS NULL AND
"SYS_ALIAS_1"."CATEGORY_ID"<>130103 AND "SYS_ALIAS_1"."CATEGORY_ID"<>130104 AND
"SYS_ALIAS_1"."CATEGORY_ID"<>130102 AND "SYS_ALIAS_1"."CATEGORY_ID"<>140102 AND
"SYS_ALIAS_1"."CATEGORY_ID"<>140101 AND ("SYS_ALIAS_1"."FEE_ID" IS NULL OR "SYS_ALIAS_1"."FEE_ID" IS
NOT NULL AND TO_NUMBER("SYS_ALIAS_1"."ORIGIN_TYPE")=701))
11 - access("SYS_ALIAS_1"."POLICY_ID"="CANCEL_APPOINT"."POLICY_ID"(+))
12 - filter(TO_NUMBER("F"."POLICY_TYPE")=1)
13 - access("SYS_ALIAS_1"."POLICY_ID"="F"."POLICY_ID")
14 - filter("PC"."NEED_PRITN"='Y')
15 - access("SYS_ALIAS_1"."CATEGORY_ID"="PC"."CATEGORY_ID")
filter("PC"."CATEGORY_ID"<>130103 AND "PC"."CATEGORY_ID"<>130104 AND "PC"."CATEGORY_ID"<>130102
AND "PC"."CATEGORY_ID"<>140102 AND "PC"."CATEGORY_ID"<>140101)
17 - access("F"."AGENT_ID"="G"."AGENT_ID"(+))
18 - access("LR"."MAIN_RECEIVER"='Y' AND "SYS_ALIAS_1"."ITEM_ID"="LR"."ITEM_ID")
20 - filter("T_COMPANY_ORGAN"."ORGAN_ID"='107')
22 - access("T_COMPANY_ORGAN"."ORGAN_ID"='107')
27 - access("T_COMPANY_ORGAN"."PARENT_ID"=NULL)
30 - access("T_POLICY_PROBLEM"."NOTICE_CODE"=:B1)
64 rows selected.
Statistics
----------------------------------------------------------
7 recursive calls
0 db block gets
1626677 consistent gets
30677 physical reads
128 redo size
2291351 bytes sent via SQL*Net to client
13277 bytes received via SQL*Net from client
1060 SQL*Net roundtrips to/from client
6 sorts (memory)
0 sorts (disk)
15878 rows processed
实际会返回15878行，但是执行计划上说返回1条记录，初学者可能会觉得是统计信息的问题(如果你觉得这个SQL跑得慢是统计信息不准，那么你就是初学者)，其实不是这样的
因为有INDEX UNIQUE SCAN ，返回1条记录是正常的(不返回1条才不正常)，另外第九步这里，它过滤条件太复杂，CBO在计算基数的时候也很容易把它算少，这里等于1
好了言归正传，这个SQL最坑爹的地方其实 是这个条件
And a.Item_Id = (Select Max(item_id)
From t_Policy_Problem
Where notice_code = a.notice_code)
这里其实相当于 t_Policy_Problem 这个表做自连接，但是这个自连接很坑爹，会导致 t_Policy_Problem 表扫描2次，从执行计划上可以看出，第九步这里它做了一个全表扫描，然后在最后28,29.30 这3步走了索引，然后回表，最后它还要被FILTER过滤 ，恩 这个地方就是 这个SQL的性能瓶颈 那么SQL 改写如下：
WITH t_Policy_Problem_w AS
(SELECT tp.*,
max(item_id) OVER (PARTITION BY notice_code)
max_item_id
FROM t_Policy_Problem tp)
select distinct decode(length(a.category_id),
5,
decode(a.origin_type, 801, 888888, 999999),
a.category_id) category_id,
a.notice_code,
a.treat_status,
lr.real_name as receiver_name,
f.send_code,
f.policy_code,
g.real_name agent_name,
f.organ_id,
f.dept_id,
a.policy_id,
a.change_id,
a.case_id,
a.group_policy_id,
a.fee_id,
a.auth_id,
a.pay_id,
cancel_appoint.appoint_time cancel_appoint_time,
a.insert_time,
a.send_time,
a.end_time,
f.agency_code,
a.REPLY_TIME,
a.REPLY_EMP_ID,
a.FIRST_DUTY,
a.NEED_SEND_PRINT,
11 source
from t_Policy_Problem_w a,
t_policy f,
t_agent g,
t_letter_receiver lr,
t_problem_category pc,
t_policy_cancel_appoint cancel_appoint
where
a.item_id=a.max_item_id
and f.agent_id = g.agent_id(+)
and a.policy_id = f.policy_id(+)
and lr.main_receiver = 'Y'
and a.category_id = pc.category_id
and a.item_id = lr.item_id
and a.policy_id = cancel_appoint.policy_id(+)
and a.policy_id is not null
and a.notice_code is not null
and a.change_id is null
and a.case_id is null
and a.group_policy_id is null
and a.origin_type not in (801, 802)
and a.pay_id is null
and a.category_id not in
(130103, 130104, 130102, 140102, 140101)
and f.policy_type = 1
and (a.fee_id is null or
(a.fee_id is not null and a.origin_type = 701))
and f.organ_id in
(select distinct organ_id
from T_COMPANY_ORGAN
start with organ_id = '107'
connect by parent_id = prior organ_id)
and pc.NEED_PRITN = 'Y'
----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)|
----------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 21241 | 5289K| | 17992 (0)|
| 1 | SORT UNIQUE | | 21241 | 5289K| 11M| 17992 (0)|
|* 2 | HASH JOIN | | 21241 | 5289K| 5192K| 17192 (1)|
|* 3 | HASH JOIN OUTER | | 21248 | 4938K| 4856K| 16727 (1)|
|* 4 | HASH JOIN OUTER | | 21248 | 4606K| 4568K| 15994 (1)|
|* 5 | HASH JOIN | | 21248 | 4316K| | 15920 (1)|
|* 6 | TABLE ACCESS FULL | T_PROBLEM_CATEGORY | 371 | 2597 | | 4 (0)|
|* 7 | HASH JOIN | | 29477 | 5786K| 5712K| 15915 (1)|
|* 8 | HASH JOIN | | 62888 | 4974K| | 9575 (1)|
| 9 | VIEW | VW_NSO_1 | 7 | 42 | | |
|* 10 | CONNECT BY WITH FILTERING | | | | | |
| 11 | NESTED LOOPS | | | | | |
|* 12 | INDEX UNIQUE SCAN | PK_T_COMPANY_ORGAN | 1 | 6 | | |
| 13 | TABLE ACCESS BY USER ROWID| T_COMPANY_ORGAN | | | | |
| 14 | NESTED LOOPS | | | | | |
| 15 | BUFFER SORT | | 7 | 70 | | |
| 16 | CONNECT BY PUMP | | | | | |
|* 17 | INDEX RANGE SCAN | T_COMPANY_ORGAN_IDX_002 | 7 | 70 | | 1 (0)|
|* 18 | TABLE ACCESS FULL | T_POLICY | 637K| 45M| | 9569 (0)|
|* 19 | VIEW | | 300K| 34M| | |
| 20 | WINDOW SORT | | 300K| 30M| 88M| 5648 (0)|
| 21 | TABLE ACCESS FULL | T_POLICY_PROBLEM | 300K| 30M| | 706 (0)|
| 22 | TABLE ACCESS FULL | T_POLICY_CANCEL_APPOINT | 86 | 1204 | | 2 (0)|
| 23 | TABLE ACCESS FULL | T_AGENT | 88982 | 1390K| | 619 (0)|
|* 24 | INDEX FAST FULL SCAN | T_LETTER_RECEIVER_IDX_001 | 300K| 4987K| | 251 (0)|
----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("A"."ITEM_ID"="LR"."ITEM_ID")
3 - access("F"."AGENT_ID"="G"."AGENT_ID"(+))
4 - access("A"."POLICY_ID"="CANCEL_APPOINT"."POLICY_ID"(+))
5 - access("A"."CATEGORY_ID"="PC"."CATEGORY_ID")
6 - filter("PC"."NEED_PRITN"='Y' AND "PC"."CATEGORY_ID"<>130103 AND "PC"."CATEGORY_ID"<>130104 AND
"PC"."CATEGORY_ID"<>130102 AND "PC"."CATEGORY_ID"<>140102 AND "PC"."CATEGORY_ID"<>140101)
7 - access("A"."POLICY_ID"="F"."POLICY_ID")
8 - access("F"."ORGAN_ID"="VW_NSO_1"."$nso_col_1")
10 - filter("T_COMPANY_ORGAN"."ORGAN_ID"='107')
12 - access("T_COMPANY_ORGAN"."ORGAN_ID"='107')
17 - access("T_COMPANY_ORGAN"."PARENT_ID"=NULL)
18 - filter(TO_NUMBER("F"."POLICY_TYPE")=1)
19 - filter("A"."ITEM_ID"="A"."MAX_ITEM_ID" AND "A"."POLICY_ID" IS NOT NULL AND "A"."NOTICE_CODE" IS NOT NULL
AND "A"."CHANGE_ID" IS NULL AND "A"."CASE_ID" IS NULL AND "A"."GROUP_POLICY_ID" IS NULL AND
TO_NUMBER("A"."ORIGIN_TYPE")<>801 AND TO_NUMBER("A"."ORIGIN_TYPE")<>802 AND "A"."PAY_ID" IS NULL AND
"A"."CATEGORY_ID"<>130103 AND "A"."CATEGORY_ID"<>130104 AND "A"."CATEGORY_ID"<>130102 AND
"A"."CATEGORY_ID"<>140102 AND "A"."CATEGORY_ID"<>140101 AND ("A"."FEE_ID" IS NULL OR "A"."FEE_ID" IS NOT NULL
AND TO_NUMBER("A"."ORIGIN_TYPE")=701))
24 - filter("LR"."MAIN_RECEIVER"='Y')
53 rows selected.
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
115995 consistent gets
42204 physical reads
0 redo size
2182416 bytes sent via SQL*Net to client
13289 bytes received via SQL*Net from client
1060 SQL*Net roundtrips to/from client
7 sorts (memory)
0 sorts (disk)
15879 rows processed
利用分析函数MAX OVER (PARTITION BY) 干掉 那个自连接，减少表访问次数，干掉那个FILTER ，现在逻辑读降低到了115995，性能提升了近15倍
这个SQL还有进一步优化的空间，另外这个SQL也还有需要改写的地方，不过那些太简单了 就不说了，其实以前盖尔发的SQL也有
And a.Item_Id = (Select Max(item_id)
From t_Policy_Problem
Where notice_code = a.notice_code)
不过当时没给他改SQL 呵呵，当时太懒了，今天第一条上班心情不错 加上时间充裕，就搞搞吧
通过这个案例，你要学到的就是自连接的优化方法，利用分析函数干掉自连接，减少表访问次数。