oracle sql优化案例1（使用组合索引）
Bad sql
SELECT T3.CONFLICT_ID,
T3.LAST_UPD,
T3.CREATED,
T3.LAST_UPD_BY,
T3.CREATED_BY,
T3.MODIFICATION_NUM,
T3.ROW_ID,
T3.ATTR_04,
T3.ATTR_03,
T2.VAL,
T3.ATTR_01,
T3.ATTR_02,
T1.NAME,
T2.VAL1
FROM user.S_ORG_EXT T1, user.CX_LOOKUP T2, user.CX_POS_LOG_INFOT3
WHERE T3.ATTR_02 = T1.PAR_ROW_ID
AND T3.ATTR_01 = T2.NAME1
AND T2.TYPE = 'PROVIDER'
AND (T3.TYPE = 'INFO')
AND (T3.ATTR_04 = :1 AND T3.ATTR_02 = :2)
原因分析：对CX_POS_LOG_INFO表全表扫描，其实统计信息也不准确，表的大小应该500M左右了
--------------------------------------------------------------------------------
| Operation | PHV/Object Name | Rows | Bytes| Cost |
--------------------------------------------------------------------------------
|SELECT STATEMENT |----- 1762745057 ----| | | 3655 |
|NESTED LOOPS | | 1 | 1K| 3655 |
| NESTED LOOPS | | 1 | 109 | 2 |
| TABLE ACCESS BY INDEX ROWID |S_ORG_EXT | 1 | 25 | 1 |
| INDEX UNIQUE SCAN |S_ORG_EXT_U3 | 1 | | 2 |
| TABLE ACCESS BY INDEX ROWID |CX_LOOKUP | 1 | 84 | 1 |
| INDEX RANGE SCAN |CX_LOOKUP_U1 | 1 | | 2 |
| TABLE ACCESS FULL |CX_POS_LOG_INFO | 1 | 1K| 3653 |
--------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
71207 consistent gets
71187 physical reads
0 redo size
1131 bytes sent via SQL*Net to client
460 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
解决思路：
手工添加组合索引，使查询走组合索引，查询从65秒下降到1秒，逻辑读从71207（556M）下降到21
create indexSIEBEL.IDX_CX_POS_LOG_INFO_U1 on SIEBEL.CX_POS_LOG_INFO (ATTR_02, ATTR_04)
tablespace SIEB_IDX
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3 Card=1 Bytes=1278)
1 0 TABLE ACCESS (BY INDEX ROWID)OF 'CX_POS_LOG_INFO' (Cost=1 Card=1 Bytes=1169)
2 1 NESTED LOOPS (Cost=3 Card=1Bytes=1278)
3 2 NESTED LOOPS (Cost=2Card=1 Bytes=109)
4 3 TABLE ACCESS (BY INDEXROWID) OF 'S_ORG_EXT' (Cost=1 Card=1Bytes=25)
5 4 INDEX (UNIQUE SCAN) OF'S_ORG_EXT_U3' (UNIQUE) (Cost=2 Card=1)
6 3 TABLE ACCESS (BY INDEXROWID) OF 'CX_LOOKUP' (Cost=1 Card=1Bytes=84)
7 6 INDEX (RANGE SCAN) OF'CX_LOOKUP_U1' (UNIQUE) (Cost=2 Card=1)
8 2 INDEX (RANGE SCAN) OF'IDX_CX_POS_LOG_INFO_U1' (NON-UNIQUE)(Cost=1 Card=93)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
18 consistent gets
0 physical reads
0 redo size
1448 bytes sent via SQL*Net to client
655 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed