今天，某數據倉庫系統的開發發來一條SQL，說跑了3個小時，嚴重拖慢了整個的跑批流程。
INSERT INTO ETL.RRR_SSSS_GGGG_INTERNAL_PTB
(RPT_ORG_ID,
ITEM_CD,
ASSET_SPOT,
LIABILITY_SPOT,
FORWARD_LONG,
FORWARD_SHORT,
ADJ_OPTION_POSITION,
EXP_POSITION,
STRUCTURAL_ASSET,
OVERS_BRCH,
ATTACH_COMPANT,
TOTAL_EXP,
EXPO_TOTAL_LIAB,
INT_EXP_LIMIT,
DATA_DATE)
SELECT '00001',
(CASE
WHEN T1.CURR_CD = 'USD' THEN
1
WHEN T1.CURR_CD = 'EUR' THEN
2
WHEN T1.CURR_CD = 'JPY' THEN
3
WHEN T1.CURR_CD = 'GBP' THEN
4
WHEN T1.CURR_CD = 'HKD' THEN
5
WHEN T1.CURR_CD = 'CHF' THEN
6
WHEN T1.CURR_CD = 'AUD' THEN
7
WHEN T1.CURR_CD = 'CAD' THEN
8
WHEN T1.CURR_CD NOT IN ('USD',
'EUR',
'JPY',
'GBP',
'HKD',
'CHF',
'AUD',
'CAD',
'GOLD') AND
(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL) >= 0 THEN
10
WHEN T1.CURR_CD NOT IN ('USD',
'EUR',
'JPY',
'GBP',
'HKD',
'CHF',
'AUD',
'CAD',
'GOLD') AND
(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL) < 0 THEN
11
END) AS ITEM_CD,
ABS(SUM(T1.SPOT_ASSET)),
ABS(SUM(T1.SPOT_LIABILITY)),
ABS(SUM(T1.FORWARD_BUY)),
ABS(SUM(T1.FORWARD_SELL)),
NULL,
SUM(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL),
SUM(T1.ASSET_STRUCTURAL),
0,
0,
SUM(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL),
SUM(T1.ASSET_STRUCTURAL),
0,
:B1
FROM (SELECT NVL(NVL(T1.CURR_CD, D1.CURR_CD), D2.CURR_CD) AS CURR_CD,
NVL(T1.SPOT_ASSET, 0) AS SPOT_ASSET,
NVL(T1.SPOT_LIABILITY, 0) AS SPOT_LIABILITY,
NVL(T1.FORWARD_BUY, 0) + NVL(D1.DBUY_VAL, 0) AS FORWARD_BUY,
-1 * (NVL(-1 * T1.FORWARD_SELL, 0) + NVL(D2.DSELL_VAL, 0)) AS FORWARD_SELL,
NVL(T1.ASSET_STRUCTURAL, 0) AS ASSET_STRUCTURAL
FROM (SELECT (CASE
WHEN T2.OBJ_ATTR_ID IS NOT NULL AND
T3.CD_ID <> 'GOLD' THEN
T2.OBJ_ATTR_ID
ELSE
T1.CURR_CD
END) AS CURR_CD,
SUM((CASE
WHEN T3.ATTR_ID = 'USD' AND
((T1.PROD_TYPE = 'A_L' AND T1.SEQ_NUM = '1') OR
T1.PROD_TYPE = 'STRUCTURE' OR
T1.PROD_TYPE = 'DEPECIATION' OR
T1.PROD_TYPE = 'COMMONACCOUNT' OR
(T1.PROD_TYPE = 'GOLD_POSITION' AND
T1.SEQ_NUM = '1')) THEN
NVL(T1.MARKET_VAL, 0)
WHEN T3.ATTR_ID <> 'USD' AND T3.CD_ID <> 'GOLD' AND
((T1.PROD_TYPE = 'A_L' AND T1.SEQ_NUM = '1') OR
T1.PROD_TYPE = 'STRUCTURE' OR
T1.PROD_TYPE = 'DEPECIATION' OR
T1.PROD_TYPE = 'COMMONACCOUNT') THEN
NVL(T1.MARKET_VAL, 0)
ELSE
0
END)) AS SPOT_ASSET,
SUM((CASE
WHEN T3.ATTR_ID = 'USD' AND
((T1.PROD_TYPE = 'A_L' AND T1.SEQ_NUM = '2') OR
(T1.PROD_TYPE = 'GOLD_POSITION' AND
T1.SEQ_NUM = '2')) THEN
NVL(T1.MARKET_VAL, 0)
WHEN T3.ATTR_ID <> 'USD' AND T3.CD_ID <> 'GOLD' AND
T1.PROD_TYPE = 'A_L' AND T1.SEQ_NUM = '2' THEN
NVL(T1.MARKET_VAL, 0)
ELSE
0
END)) AS SPOT_LIABILITY,
SUM((CASE
WHEN T1.PROD_TYPE = 'FX_Unsettled' AND
T1.SEQ_NUM IN ('1', '3') AND
T1.EXT_PRODUCT_TIER2 = 'PS_000000035' AND
T1.BUSINESS_PK NOT LIKE 'CAP_40604%' THEN
NVL(T1.MARKET_VAL, 0)
ELSE
0
END)) AS FORWARD_BUY,
SUM((CASE
WHEN T1.PROD_TYPE = 'FX_Unsettled' AND
T1.SEQ_NUM IN ('2', '4') AND
T1.EXT_PRODUCT_TIER2 = 'PS_000000035' AND
T1.BUSINESS_PK NOT LIKE 'CAP_40604%' THEN
NVL(T1.MARKET_VAL, 0)
ELSE
0
END)) AS FORWARD_SELL,
SUM((CASE
WHEN T1.PROD_TYPE = 'STRUCTURE' THEN
NVL(T1.MARKET_VAL, 0) * (-1)
ELSE
0
END)) AS ASSET_STRUCTURAL
FROM ETL.MIM_RRRR_EEEE_PPP T1
LEFT JOIN ETL.MID_REF_COD_MAP_TBL T2
ON T2.SRC_CODE_ID = 'SRC_COMM_CD'
AND T1.CURR_CD = T2.SRC_ATTR_ID
LEFT JOIN ETL.MIM_RRR_CCC_AAA_TTT T3
ON T3.CODE_TYPE = 'CURR_TYP'
AND T3.CD_ID <> 'COMM'
AND (CASE
WHEN T2.OBJ_ATTR_ID IS NOT NULL THEN
T2.OBJ_ATTR_ID
ELSE
T1.CURR_CD
END) = T3.ATTR_ID
WHERE T1.DATA_DATE = :B1
AND T1.EFFECTIVE_OR_NOT = 'Y'
AND T1.PROD_TYPE <> 'GOLD_SPOT'
AND T3.CD_ID <> 'GOLD'
GROUP BY (CASE
WHEN T2.OBJ_ATTR_ID IS NOT NULL AND
T3.CD_ID <> 'GOLD' THEN
T2.OBJ_ATTR_ID
ELSE
T1.CURR_CD
END)) T1
LEFT JOIN (SELECT T1.CCY_CD AS CURR_CD,
SUM(NVL(T1.DAY_CR_BAL, 0) *
NVL(T2.EXCH_RATE, 1)) AS DBUY_VAL
FROM MIM_TTT_DDDDD_BOOK_PTB T1
LEFT JOIN ETL.MIM_RRR_CCCC_EE_PPP T2
ON T1.CCY_CD = T2.NUMERATOR_CURR_CD
AND T2.DATA_DATE = :B1
INNER JOIN ETL.MIM_RRR_CCC_AAA_TTT T3
ON T1.CCY_CD = T3.ATTR_ID
AND T3.CODE_TYPE = 'CURR_TYP'
WHERE T1.DATA_DATE = :B1
AND T1.CCY_CD NOT LIKE '%01'
AND T1.CCY_CD <> 'CNY'
AND T1.INTER_ORG_ID = 'GLS9_T'
AND T1.ACCTING_COA_ID LIKE '9521%'
AND T1.ACCTING_INTERIM =
SUBSTR(T1.ACCTING_DT, 1, 4) || '-' ||
SUBSTR(T1.ACCTING_DT, 5, 2)
GROUP BY T1.CCY_CD, NVL(T2.EXCH_RATE, 1)) D1
ON T1.CURR_CD = D1.CURR_CD
LEFT JOIN (SELECT T1.CCY_CD AS CURR_CD,
SUM(CASE
WHEN T1.ACCTING_COA_ID LIKE '9522%' THEN
NVL(T1.DAY_CR_BAL, 0) * NVL(T2.EXCH_RATE, 1)
ELSE
-1 * NVL(T1.DAY_CR_BAL, 0) *
NVL(T2.EXCH_RATE, 1)
END) AS DSELL_VAL
FROM MIM_TTT_DDDDD_BOOK_PTB T1
LEFT JOIN ETL.MIM_RRR_CCCC_EE_PPP T2
ON T1.CCY_CD = T2.NUMERATOR_CURR_CD
AND T2.DATA_DATE = :B1
INNER JOIN ETL.MIM_RRR_CCC_AAA_TTT T3
ON T1.CCY_CD = T3.ATTR_ID
AND T3.CODE_TYPE = 'CURR_TYP'
WHERE T1.DATA_DATE = :B1
AND T1.CCY_CD NOT LIKE '%01'
AND T1.CCY_CD <> 'CNY'
AND T1.INTER_ORG_ID = 'GLS9_T'
AND (T1.ACCTING_COA_ID LIKE '9522%' OR
T1.ACCTING_COA_ID LIKE '2009%')
AND T1.ACCTING_INTERIM =
SUBSTR(T1.ACCTING_DT, 1, 4) || '-' ||
SUBSTR(T1.ACCTING_DT, 5, 2)
GROUP BY T1.CCY_CD) D2
ON T1.CURR_CD = D2.CURR_CD) T1
GROUP BY (CASE
WHEN T1.CURR_CD = 'USD' THEN
1
WHEN T1.CURR_CD = 'EUR' THEN
2
WHEN T1.CURR_CD = 'JPY' THEN
3
WHEN T1.CURR_CD = 'GBP' THEN
4
WHEN T1.CURR_CD = 'HKD' THEN
5
WHEN T1.CURR_CD = 'CHF' THEN
6
WHEN T1.CURR_CD = 'AUD' THEN
7
WHEN T1.CURR_CD = 'CAD' THEN
8
WHEN T1.CURR_CD NOT IN ('USD',
'EUR',
'JPY',
'GBP',
'HKD',
'CHF',
'AUD',
'CAD',
'GOLD') AND
(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL) >= 0 THEN
10
WHEN T1.CURR_CD NOT IN ('USD',
'EUR',
'JPY',
'GBP',
'HKD',
'CHF',
'AUD',
'CAD',
'GOLD') AND
(T1.SPOT_ASSET + T1.SPOT_LIABILITY + T1.FORWARD_BUY +
T1.FORWARD_SELL) < 0 THEN
11
END)
Plan hash value: 2210955645
-------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
-------------------------------------------------------------------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | | | 17493 (100)| | | |
| 1 | LOAD TABLE CONVENTIONAL | | | | | | | |
| 2 | HASH GROUP BY | | 1 | 117 | 17493 (1)| 00:03:30 | | |
| 3 | HASH JOIN RIGHT OUTER | | 111 | 12987 | 17492 (1)| 00:03:30 | | |
| 4 | VIEW | | 1 | 17 | 881 (1)| 00:00:11 | | |
| 5 | SORT GROUP BY | | 1 | 97 | 881 (1)| 00:00:11 | | |
| 6 | HASH JOIN | | 1 | 97 | 880 (0)| 00:00:11 | | |
| 7 | HASH JOIN OUTER | | 1 | 78 | 877 (0)| 00:00:11 | | |
| 8 | TABLE ACCESS BY GLOBAL INDEX ROWID | MIM_TTT_DDDDD_BOOK_PTB | 1 | 54 | 874 (0)| 00:00:11 | ROWID | ROWID |
| 9 | INDEX SKIP SCAN | MIM_TTT_DDDDD_BOOK_PK | 1 | | 873 (0)| 00:00:11 | | |
| 10 | PARTITION LIST SINGLE | | 35 | 840 | 3 (0)| 00:00:01 | KEY | KEY |
| 11 | TABLE ACCESS FULL | MIM_RRR_CCCC_EE_PPP | 35 | 840 | 3 (0)| 00:00:01 | KEY | KEY |
| 12 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 218 | 4142 | 3 (0)| 00:00:01 | | |
| 13 | HASH JOIN RIGHT OUTER | | 111 | 11100 | 16611 (1)| 00:03:20 | | |
| 14 | VIEW | | 1 | 17 | 442 (1)| 00:00:06 | | |
| 15 | SORT GROUP BY | | 1 | 97 | 442 (1)| 00:00:06 | | |
| 16 | HASH JOIN | | 1 | 97 | 441 (0)| 00:00:06 | | |
| 17 | HASH JOIN OUTER | | 1 | 78 | 438 (0)| 00:00:06 | | |
| 18 | TABLE ACCESS BY GLOBAL INDEX ROWID| MIM_TTT_DDDDD_BOOK_PTB | 1 | 54 | 435 (0)| 00:00:06 | ROWID | ROWID |
| 19 | INDEX SKIP SCAN | MIM_TTT_DDDDD_BOOK_PK | 1 | | 434 (0)| 00:00:06 | | |
| 20 | PARTITION LIST SINGLE | | 35 | 840 | 3 (0)| 00:00:01 | KEY | KEY |
| 21 | TABLE ACCESS FULL | MIM_RRR_CCCC_EE_PPP | 35 | 840 | 3 (0)| 00:00:01 | KEY | KEY |
| 22 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 218 | 4142 | 3 (0)| 00:00:01 | | |
| 23 | VIEW | | 111 | 9213 | 16169 (1)| 00:03:15 | | |
| 24 | SORT GROUP BY | | 111 | 14208 | 16169 (1)| 00:03:15 | | |
| 25 | HASH JOIN | | 4700 | 587K| 16168 (1)| 00:03:15 | | |
| 26 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 203 | 5075 | 3 (0)| 00:00:01 | | |
| 27 | HASH JOIN RIGHT OUTER | | 10385 | 1044K| 16165 (1)| 00:03:14 | | |
| 28 | TABLE ACCESS FULL | MID_REF_COD_MAP_TBL | 14 | 336 | 3 (0)| 00:00:01 | | |
| 29 | PARTITION LIST SINGLE | | 10385 | 801K| 16162 (1)| 00:03:14 | KEY | KEY |
| 30 | TABLE ACCESS FULL | MIM_RRRR_EEEE_PPP | 10385 | 801K| 16162 (1)| 00:03:14 | KEY | KEY |
-------------------------------------------------------------------------------------------------------------------------------------
這個執行計劃是通過我們寫的一個工具抓出來的（還不如F5）沒有謂詞信息和統計信息。所以要作優化一定要用explain plan for來取執行計劃，當然plsql developer11之後的版本也可以顯示謂詞信息和統計信息了。
先獲取一下 這個SQL裏面的表信息和索引信息
MIM_TTT_DDDDD_BOOK_PTB 311946106 44469.19MB
MIM_RRR_CCCC_EE_PPP 15084 75.63MB
MIM_RRR_CCC_AAA_TTT 450 0.06MB
alter table ETL.MIM_TTT_DDDDD_BOOK_PTB
add constraint MIM_TTT_DDDDD_BOOK_PTB_PK primary key (ACCTING_DT, ACCTING_INTERIM, CCY_CD, ACCTING_COA_ID, GL_SRC_CD, INTER_ORG_ID, DATA_DATE)
using index
tablespace ETL_INDEX_TS
pctfree 10
initrans 2
maxtrans 255
storage
(
initial 64K
next 1M
minextents 1
maxextents unlimited
);
針對長SQL，我還是習慣性找大表【小表怎麼掃描都不會引起性能問題】
MIM_TTT_DDDDD_BOOK_PTB是這個SQL裏面唯一個大表，
出現問題的部分基本上就是[大表所在部分]
這段SQL單獨拿出來分析
explain plan for
SELECT T1.CCY_CD AS CURR_CD,
SUM(CASE
WHEN T1.ACCTING_COA_ID LIKE '9522%' THEN
NVL(T1.DAY_CR_BAL, 0) * NVL(T2.EXCH_RATE, 1)
ELSE
-1 * NVL(T1.DAY_CR_BAL, 0) * NVL(T2.EXCH_RATE, 1)
END) AS DSELL_VAL
FROM etl.MIM_TTT_DDDDD_BOOK_PTB T1
LEFT JOIN ETL.MIM_RRR_CCCC_EE_PPP T2
ON T1.CCY_CD = T2.NUMERATOR_CURR_CD
AND T2.DATA_DATE = date '2017-01-10'
INNER JOIN ETL.MIM_RRR_CCC_AAA_TTT T3
ON T1.CCY_CD = T3.ATTR_ID
AND T3.CODE_TYPE = 'CURR_TYP'
WHERE T1.DATA_DATE = date
'2017-01-10'
AND T1.CCY_CD NOT LIKE '%01'
AND T1.CCY_CD <> 'CNY'
AND T1.INTER_ORG_ID = 'GLS9_T'
AND (T1.ACCTING_COA_ID LIKE '9522%' OR T1.ACCTING_COA_ID LIKE '2009%')
AND T1.ACCTING_INTERIM =
SUBSTR(T1.ACCTING_DT, 1, 4) || '-' || SUBSTR(T1.ACCTING_DT, 5, 2)
GROUP BY T1.CCY_CD;
select * from table(dbms_xplan.display);
Plan hash value: 3749582889
--------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
--------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 97 | 881 (1)| 00:00:11 | | |
| 1 | HASH GROUP BY | | 1 | 97 | 881 (1)| 00:00:11 | | |
|* 2 | HASH JOIN | | 1 | 97 | 880 (0)| 00:00:11 | | |
|* 3 | HASH JOIN OUTER | | 1 | 78 | 877 (0)| 00:00:11 | | |
| 4 | TABLE ACCESS BY GLOBAL INDEX ROWID| MIM_TTT_DDDDD_BOOK_PTB | 1 | 54 | 874 (0)| 00:00:11 | 448 | 448 |
|* 5 | INDEX SKIP SCAN | MIM_TTT_DDDDD_BOOK_PK | 1 | | 873 (0)| 00:00:11 | | |
| 6 | PARTITION LIST SINGLE | | 34 | 816 | 3 (0)| 00:00:01 | KEY | KEY |
|* 7 | TABLE ACCESS FULL | MIM_RRR_CCCC_EE_PPP | 34 | 816 | 3 (0)| 00:00:01 | 448 | 448 |
|* 8 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 218 | 4142 | 3 (0)| 00:00:01 | | |
--------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("T1"."CCY_CD"="T3"."ATTR_ID")
3 - access("T1"."CCY_CD"="T2"."NUMERATOR_CURR_CD"(+))
5 - access("T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd
hh24:mi:ss'))
filter("T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "T1"."CCY_CD"<>'CNY' AND ("T1"."ACCTING_COA_ID" LIKE '9522%' OR "T1"."ACCTING_COA_ID" LIKE '2009%')
AND "T1"."ACCTING_INTERIM"=SUBSTR("T1"."ACCTING_DT",1,4)||'-'||SUBSTR("T1"."ACCTING_DT",5,2) AND "T1"."CCY_CD" NOT LIKE
'%01')
7 - filter("T2"."NUMERATOR_CURR_CD"(+)<>'CNY')
8 - filter("T3"."CODE_TYPE"='CURR_TYP' AND "T3"."ATTR_ID"<>'CNY')
從執行計劃可以看出這個SQL引起性能瓶頸的部分就是第5步 INDEX SKIP SCAN | MID_TXN_DAILY_BOOK_PK
這個主鍵索引有7個列。INDEX SKIP SCAN 的引導列INTER_ORG_ID在索引的第6個列，跳掃需要跳躍引導列（ACCTING_DT）基數（DISTINCT_KEYS）次，
而ACCTING_DT列的基數非常高，所以索引需要跳躍的次數很多。
而且索引跳躍掃描所使用的引導列INTER_ORG_ID列的基數非常低，類似機構號這種參數列，一個值對應了表中很多行，會對回表產生很大的壓力
在執行計劃第5步的謂詞信息filter裏面我們看到了："T1"."ACCTING_COA_ID" LIKE '9522%' OR "T1"."ACCTING_COA_ID" LIKE '2009%'這個條件
"T1"."ACCTING_COA_ID"這個列在索引的第4列，同樣會產生跳躍掃描，但是ACCTING_COA_ID的基數高，回表壓力少，所以性能肯定比上一個好。
然而我們看執行計劃的第5步的謂詞信息，這個條件沒有出現在access裏面，而是出現在filter裏面，所以這個列壓根沒起到引導作用，只是一個簡單的過濾作用
所以引起性能問題的根本原因就是AND ("T1"."ACCTING_COA_ID" LIKE '9522%' OR "T1"."ACCTING_COA_ID" LIKE '2009%')這種寫法導致了條件無法展開，只能走過濾
我們嘗試使用hint /*+ use_concat */展開OR的條件，得到下面的執行計劃（相關hint /*+ use_concat */ or條件展開 /*+ no_expand */ 條件合併）
Plan hash value: 3949042395
---------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
---------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 97 | 883 (1)| 00:00:11 | | |
| 1 | HASH GROUP BY | | 1 | 97 | | | | |
| 2 | CONCATENATION | | | | | | | |
|* 3 | HASH JOIN | | 1 | 97 | 441 (0)| 00:00:06 | | |
|* 4 | HASH JOIN OUTER | | 1 | 78 | 438 (0)| 00:00:06 | | |
| 5 | TABLE ACCESS BY GLOBAL INDEX ROWID| MIM_TTT_DDDDD_BOOK_PTB | 1 | 54 | 435 (0)| 00:00:06 | 448 | 448 |
|* 6 | INDEX SKIP SCAN | MIM_TTT_DDDDD_BOOK_PK | 1 | | 434 (0)| 00:00:06 | | |
| 7 | PARTITION LIST SINGLE | | 34 | 816 | 3 (0)| 00:00:01 | KEY | KEY |
|* 8 | TABLE ACCESS FULL | MIM_RRR_CCCC_EE_PPP | 34 | 816 | 3 (0)| 00:00:01 | 448 | 448 |
|* 9 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 218 | 4142 | 3 (0)| 00:00:01 | | |
|* 10 | HASH JOIN | | 1 | 97 | 441 (0)| 00:00:06 | | |
|* 11 | HASH JOIN OUTER | | 1 | 78 | 438 (0)| 00:00:06 | | |
| 12 | TABLE ACCESS BY GLOBAL INDEX ROWID| MIM_TTT_DDDDD_BOOK_PTB | 1 | 54 | 435 (0)| 00:00:06 | 448 | 448 |
|* 13 | INDEX SKIP SCAN | MIM_TTT_DDDDD_BOOK_PK | 1 | | 434 (0)| 00:00:06 | | |
| 14 | PARTITION LIST SINGLE | | 34 | 816 | 3 (0)| 00:00:01 | KEY | KEY |
|* 15 | TABLE ACCESS FULL | MIM_RRR_CCCC_EE_PPP | 34 | 816 | 3 (0)| 00:00:01 | 448 | 448 |
|* 16 | TABLE ACCESS FULL | MIM_RRR_CCC_AAA_TTT | 218 | 4142 | 3 (0)| 00:00:01 | | |
---------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("T1"."CCY_CD"="T3"."ATTR_ID")
4 - access("T1"."CCY_CD"="T2"."NUMERATOR_CURR_CD"(+))
6 - access("T1"."ACCTING_COA_ID" LIKE '2009%' AND "T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE('
2017-01-10 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
filter("T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "T1"."ACCTING_COA_ID" LIKE '2009%' AND "T1"."CCY_CD"<>'CNY' AND
"T1"."ACCTING_INTERIM"=SUBSTR("T1"."ACCTING_DT",1,4)||'-'||SUBSTR("T1"."ACCTING_DT",5,2) AND "T1"."CCY_CD" NOT LIKE
'%01')
8 - filter("T2"."DATA_DATE"(+)=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND
"T2"."NUMERATOR_CURR_CD"(+)<>'CNY')
9 - filter("T3"."CODE_TYPE"='CURR_TYP' AND "T3"."ATTR_ID"<>'CNY')
10 - access("T1"."CCY_CD"="T3"."ATTR_ID")
11 - access("T1"."CCY_CD"="T2"."NUMERATOR_CURR_CD"(+))
13 - access("T1"."ACCTING_COA_ID" LIKE '9522%' AND "T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE('
2017-01-10 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
filter("T1"."INTER_ORG_ID"='GLS9_T' AND "T1"."DATA_DATE"=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "T1"."ACCTING_COA_ID" LIKE '9522%' AND "T1"."CCY_CD"<>'CNY' AND
"T1"."ACCTING_INTERIM"=SUBSTR("T1"."ACCTING_DT",1,4)||'-'||SUBSTR("T1"."ACCTING_DT",5,2) AND "T1"."CCY_CD" NOT LIKE
'%01' AND LNNVL("T1"."ACCTING_COA_ID" LIKE '2009%'))
15 - filter("T2"."DATA_DATE"(+)=TO_DATE(' 2017-01-10 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND
"T2"."NUMERATOR_CURR_CD"(+)<>'CNY')
16 - filter("T3"."CODE_TYPE"='CURR_TYP' AND "T3"."ATTR_ID"<>'CNY')
從謂詞第6步和第13步可以看出執行計劃是按照我們的想法將OR條件展開index skip scan走正確的引導列，性能提升！！！！
其實這個SQL還可以進一步優化。重新創建以ACCTING_COA_ID爲引導列的組合索引，當然生產上不讓建索引，我就不往下進行了。
優化到這裏我們總結一下union和or互換的情況
1）OR條件會導致無法使用條件列的索引。
2）使用HINT /*+ use_concat */ 展開OR的條件，會有一定概率無法使用到條件列索引。
3）當SQL語句中，or 條件上面有一個子查詢（OR EXISTE ......）的時候，執行計劃中會產生FILTER 。這個FILTER會產生很大的性能問題。這種情況只能通過使用UNION代替OR的改寫來優化FILTER。
4）儘量使用UNION代替OR，可以避免很多坑。
5）UNION和OR是等價的.但是UNION效率太低。可以使用UNION ALL配合LNNVL來等價改寫OR。
"T1"."ACCTING_COA_ID" LIKE '2009%'
UNION ALL
"T1"."ACCTING_COA_ID" LIKE '9522%' AND LNNVL("T1"."ACCTING_COA_ID" LIKE '2009%')