?上周五要下班的時候，蓋爾發來一個SQL

select tpc.policy_id,tcm.policy_code,tpf.organ_id,to_char(tpf.insert_time, 'YYYY-MM-DD') As insert_time,tpc.change_id,d.policy_code,e.company_name,f.real_name,tpf.fee_type,sum(tpf.pay_balance) as pay_balance,c.actual_type,tpc.notice_code,d.policy_type,g.mode_name as pay_modefrom t_policy_change tpc,t_contract_master tcm,t_policy_fee tpf,t_fee_type c,t_contract_master d,t_company_customer e,t_customer f,t_pay_mode gwhere tpc.change_id = tpf.change_idand tpf.policy_id = d.policy_idand tcm.policy_id = tpc.policy_idand tpf.receiv_status = 1 and tpf.fee_status = 1and tpf.payment_id is nulland tpf.fee_type = c.type_idand tpf.pay_mode = g.mode_idand d.company_id = e.company_id(+)and d.applicant_id = f.customer_id(+)and tpf.organ_id in(select organ_idfrom t_company_organstart with organ_id = '101'connect by prior organ_id = parent_id)group by tpc.policy_id,tpc.change_id,tpf.fee_type,to_char(tpf.insert_time, 'YYYY-MM-DD'),c.actual_type,d.policy_code,g.mode_name,e.company_name,f.real_name,tpc.notice_code,d.policy_type,tpf.organ_id,tcm.policy_codeorder by change_id, fee_typeSQL> select * from table(dbms_xplan.display);PLAN_TABLE_OUTPUT ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| ---------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 45962 | 11M| | 45650 (0)| | 1 | SORT GROUP BY | | 45962 | 11M| 23M| 45650 (0)| |* 2 | HASH JOIN | | 45962 | 11M| | 43908 (0)| | 3 | INDEX FULL SCAN | T_FEE_TYPE_IDX_003 | 106 | 636 | | 1 (0)| | 4 | NESTED LOOPS OUTER | | 45962 | 11M| | 43906 (0)| |* 5 | HASH JOIN | | 45962 | 7271K| 6824K| 43905 (0)| | 6 | NESTED LOOPS | | 45961 | 6283K| | 42312 (0)| |* 7 | HASH JOIN SEMI | | 45961 | 5655K| 50M| 33120 (1)| |* 8 | HASH JOIN OUTER | | 400K| 45M| 44M| 32315 (1)| |* 9 | HASH JOIN | | 400K| 39M| 27M| 26943 (0)| |* 10 | HASH JOIN | | 400K| 23M| | 16111 (0)| | 11 | TABLE ACCESS FULL | T_PAY_MODE | 25 | 525 | | 2 (0)| |* 12 | TABLE ACCESS FULL | T_POLICY_FEE | 400K| 15M| | 16107 (0)| | 13 | TABLE ACCESS FULL | T_CONTRACT_MASTER | 1136K| 46M| | 9437 (0)| | 14 | VIEW | index_join_007 | 2028K| 30M| | | |* 15 | HASH JOIN | | 400K| 45M| 44M| 32315 (1)| | 16 | INDEX FAST FULL SCAN | PK_T_CUSTOMER | 2028K| 30M| | 548 (0)| | 17 | INDEX FAST FULL SCAN | IDX_CUSTOMER__BIR_REAL_GEN | 2028K| 30M| | 548 (0)| | 18 | VIEW | VW_NSO_1 | 7 | 42 | | | |* 19 | CONNECT BY WITH FILTERING | | | | | | | 20 | NESTED LOOPS | | | | | | |* 21 | INDEX UNIQUE SCAN | PK_T_COMPANY_ORGAN | 1 | 6 | | | | 22 | TABLE ACCESS BY USER ROWID| T_COMPANY_ORGAN | | | | | | 23 | NESTED LOOPS | | | | | | | 24 | BUFFER SORT | | 7 | 70 | | | | 25 | CONNECT BY PUMP | | | | | | |* 26 | INDEX RANGE SCAN | T_COMPANY_ORGAN_IDX_002 | 7 | 70 | | 1 (0)| | 27 | TABLE ACCESS BY INDEX ROWID | T_POLICY_CHANGE | 1 | 14 | | 2 (50)| |* 28 | INDEX UNIQUE SCAN | PK_T_POLICY_CHANGE | 1 | | | 1 (0)| | 29 | INDEX FAST FULL SCAN | IDX1_ACCEPT_DATE | 1136K| 23M| | 899 (0)| | 30 | TABLE ACCESS BY INDEX ROWID | T_COMPANY_CUSTOMER | 1 | 90 | | 2 (50)| |* 31 | INDEX UNIQUE SCAN | PK_T_COMPANY_CUSTOMER | 1 | | | | ----------------------------------------------------------------------------------------------------------------Predicate Information (identified by operation id): ---------------------------------------------------2 - access("TPF"."FEE_TYPE"="C"."TYPE_ID")5 - access("TCM"."POLICY_ID"="TPC"."POLICY_ID")7 - access("TPF"."ORGAN_ID"="VW_NSO_1"."$nso_col_1")8 - access("D"."APPLICANT_ID"="F"."CUSTOMER_ID"(+))9 - access("TPF"."POLICY_ID"="D"."POLICY_ID")10 - access("TPF"."PAY_MODE"="G"."MODE_ID")12 - filter("TPF"."CHANGE_ID" IS NOT NULL AND TO_NUMBER("TPF"."RECEIV_STATUS")=1 AND "TPF"."FEE_STATUS"=1 AND"TPF"."PAYMENT_ID" IS NULL)15 - access("indexjoin_alias_012".ROWID="indexjoin_alias_011".ROWID)19 - filter("T_COMPANY_ORGAN"."ORGAN_ID"='101')21 - access("T_COMPANY_ORGAN"."ORGAN_ID"='101')26 - access("T_COMPANY_ORGAN"."PARENT_ID"=NULL)28 - access("TPC"."CHANGE_ID"="TPF"."CHANGE_ID")31 - access("D"."COMPANY_ID"="E"."COMPANY_ID"(+))55 rows selectedStatistics ----------------------------------------------------------21 recursive calls0 db block gets125082 consistent gets21149 physical reads0 redo size2448 bytes sent via SQL*Net to client656 bytes received via SQL*Net from client2 SQL*Net roundtrips to/from client4 sorts (memory)0 sorts (disk)11 rows processed

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這個SQL要21秒才能跑完，邏輯讀12W左右，問我能不能優化。優化這個SQL我只花了1分鐘左右的時間，因為太簡單了
你們看這個SQL是典型的JOIN，對付這種SQL肯定要讓表走索引，但是從執行計劃上看有個1千萬行的表T_CONTRACT_MASTER走的是全表掃描，
T_POLICY_FEE 這個400W行的表也是走全表掃描，那么它不慢才怪呢，然后SQL的過濾條件有個 in 子查詢
?????? (select
???????? organ_id
????????? from t_company_organ
???????? start with organ_id = '101'
??????? connect by prior organ_id = parent_id)
從執行計劃上看，CBO對這兒子查詢進行了unnest，因為通常情況下CBO認為子查詢被unnest之后性能好于filter???????

于是我讓蓋爾查詢 子查詢返回多少行????????
select? organ_id
????????? from t_company_organ
???????? start with organ_id = '101'
??????? connect by prior organ_id = parent_id?? ---蓋爾說它返回1行????????

對于子查詢，如果它返回數據很少(這里返回1行)，那么可以讓它走filter, 而且filter基本上是在SQL最后去階段執行，這樣t_policy_fee就可以走索引了
所以我給這個子查詢加了個HINT，禁止子查詢擴展

select tpc.policy_id,tcm.policy_code,tpf.organ_id,to_char(tpf.insert_time, 'YYYY-MM-DD') As insert_time,tpc.change_id,d.policy_code,e.company_name,f.real_name,tpf.fee_type,sum(tpf.pay_balance) as pay_balance,c.actual_type,tpc.notice_code,d.policy_type,g.mode_name as pay_modefrom t_policy_change tpc,t_contract_master tcm,t_policy_fee tpf,t_fee_type c,t_contract_master d,t_company_customer e,t_customer f,t_pay_mode gwhere tpc.change_id = tpf.change_idand tpf.policy_id = d.policy_idand tcm.policy_id = tpc.policy_idand tpf.receiv_status = '1' ---這里原來沒引號，是開發那SB搞忘了寫'',我讓蓋爾添加上了，不添加上就沒法用索引and tpf.fee_status = 1and tpf.payment_id is nulland tpf.fee_type = c.type_idand tpf.pay_mode = g.mode_idand d.company_id = e.company_id(+)and d.applicant_id = f.customer_id(+)and tpf.organ_id in(select /*+ no_unnest */ --此處的HINT后加的organ_idfrom t_company_organstart with organ_id = '101'connect by prior organ_id = parent_id)group by tpc.policy_id,tpc.change_id,tpf.fee_type,to_char(tpf.insert_time, 'YYYY-MM-DD'),c.actual_type,d.policy_code,g.mode_name,e.company_name,f.real_name,tpc.notice_code,d.policy_type,tpf.organ_id,tcm.policy_codeorder by change_id, fee_typeSQL> select * from table(dbms_xplan.display);PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| -------------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 20026 | 4928K| | 68615 (30)| | 1 | SORT GROUP BY | | 20026 | 4928K| 10M| 28563 (0)| |* 2 | FILTER | | | | | | | 3 | NESTED LOOPS | | 20026 | 4928K| | 27812 (0)| | 4 | NESTED LOOPS | | 20026 | 4498K| | 23807 (0)| | 5 | NESTED LOOPS OUTER | | 20026 | 4224K| | 19802 (0)| | 6 | NESTED LOOPS OUTER | | 20026 | 3911K| | 15797 (0)| | 7 | NESTED LOOPS | | 20026 | 2151K| | 15796 (0)| |* 8 | HASH JOIN | | 20026 | 1310K| | 11791 (0)| | 9 | INDEX FULL SCAN | T_FEE_TYPE_IDX_003 | 106 | 636 | | 1 (0)| |* 10 | HASH JOIN | | 20026 | 1192K| | 11789 (0)| | 11 | TABLE ACCESS FULL | T_PAY_MODE | 25 | 525 | | 2 (0)| |* 12 | TABLE ACCESS BY INDEX ROWID| T_POLICY_FEE | 20026 | 782K| | 11786 (0)| |* 13 | INDEX RANGE SCAN | IDX_POLICY_FEE__RECEIV_STATUS | 1243K| | | 10188 (0)| | 14 | TABLE ACCESS BY INDEX ROWID | T_CONTRACT_MASTER | 1 | 43 | | 2 (50)| |* 15 | INDEX UNIQUE SCAN | PK_T_CONTRACT_MASTER | 1 | | | 1 (0)| | 16 | TABLE ACCESS BY INDEX ROWID | T_COMPANY_CUSTOMER | 1 | 90 | | 2 (50)| |* 17 | INDEX UNIQUE SCAN | PK_T_COMPANY_CUSTOMER | 1 | | | | | 18 | TABLE ACCESS BY INDEX ROWID | T_CUSTOMER | 1 | 16 | | 2 (50)| |* 19 | INDEX UNIQUE SCAN | PK_T_CUSTOMER | 1 | | | 1 (0)| | 20 | TABLE ACCESS BY INDEX ROWID | T_POLICY_CHANGE | 1 | 14 | | 2 (50)| |* 21 | INDEX UNIQUE SCAN | PK_T_POLICY_CHANGE | 1 | | | 1 (0)| | 22 | TABLE ACCESS BY INDEX ROWID | T_CONTRACT_MASTER | 1 | 22 | | 2 (50)| |* 23 | INDEX UNIQUE SCAN | PK_T_CONTRACT_MASTER | 1 | | | 1 (0)| |* 24 | FILTER | | | | | | |* 25 | CONNECT BY WITH FILTERING | | | | | | | 26 | NESTED LOOPS | | | | | | |* 27 | INDEX UNIQUE SCAN | PK_T_COMPANY_ORGAN | 1 | 6 | | | | 28 | TABLE ACCESS BY USER ROWID | T_COMPANY_ORGAN | | | | | | 29 | NESTED LOOPS | | | | | | | 30 | BUFFER SORT | | 7 | 70 | | | | 31 | CONNECT BY PUMP | | | | | | |* 32 | INDEX RANGE SCAN | T_COMPANY_ORGAN_IDX_002 | 7 | 70 | | 1 (0)| --------------------------------------------------------------------------------------------------------------------Predicate Information (identified by operation id): ---------------------------------------------------2 - filter( EXISTS (SELECT /*+ NO_UNNEST */ 0 FROM "T_COMPANY_ORGAN" "T_COMPANY_ORGAN" WHERE"T_COMPANY_ORGAN"."PARENT_ID"=NULL AND ("T_COMPANY_ORGAN"."ORGAN_ID"=:B1)))8 - access("SYS_ALIAS_1"."FEE_TYPE"="C"."TYPE_ID")10 - access("SYS_ALIAS_1"."PAY_MODE"="G"."MODE_ID")12 - filter("SYS_ALIAS_1"."CHANGE_ID" IS NOT NULL AND "SYS_ALIAS_1"."FEE_STATUS"=1 AND "SYS_ALIAS_1"."PAYMENT_ID"IS NULL)13 - access("SYS_ALIAS_1"."RECEIV_STATUS"='1')15 - access("SYS_ALIAS_1"."POLICY_ID"="D"."POLICY_ID")17 - access("D"."COMPANY_ID"="E"."COMPANY_ID"(+))19 - access("D"."APPLICANT_ID"="F"."CUSTOMER_ID"(+))21 - access("TPC"."CHANGE_ID"="SYS_ALIAS_1"."CHANGE_ID")23 - access("TCM"."POLICY_ID"="TPC"."POLICY_ID")24 - filter("T_COMPANY_ORGAN"."ORGAN_ID"=:B1)25 - filter("T_COMPANY_ORGAN"."ORGAN_ID"='101')27 - access("T_COMPANY_ORGAN"."ORGAN_ID"='101')32 - access("T_COMPANY_ORGAN"."PARENT_ID"=NULL)58 rows selected.Statistics ----------------------------------------------------------0 recursive calls0 db block gets2817 consistent gets0 physical reads0 redo size2268 bytes sent via SQL*Net to client656 bytes received via SQL*Net from client2 SQL*Net roundtrips to/from client40 sorts (memory)0 sorts (disk)9 rows processed

最終這個SQL能在1秒以內跑完，邏輯讀下降到2817 ，到此我就沒繼續優化了，這個時候停止優化吧，別的了強迫優化癥
這個優化案例很簡單，我都不好意思貼在博客上，通過這個文章你要學到的就是，如果子查詢返回數據很少，那么不妨讓它走filter????????

轉載于:https://www.cnblogs.com/hehe520/archive/2011/11/29/6330557.html

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