有朋友问我一个update语句，下面两种写法哪个性能更高，一个是没HINT的，一个是有HINT的
UPDATE CS_PERFORMANCE_CURRENT C
SET C.PERFORMANCE_SCORE = '0.00', C.ASSESS_DESC = '劳动纪律考核'
WHERE C.TARGET_MODE_SEQ_ID =
(SELECT D.SEQ_ID
FROM CS_TARGET_MODEL_REL D, CS_AREA A
WHERE D.ASSESS_ID = 1265
AND C.TARGET_MODE_SEQ_ID = D.SEQ_ID
AND D.STAFF_ID = 8
AND C.COM_DATE = TO_DATE('20110801','YYYYMMDD')
AND D.TARGET_MODEL_ID = 332
AND D.STATE = TO_CHAR(2)
AND D.AREA_ID = A.AREA_ID
AND A.AREA_NAME = '永兴支局');
Plan hash value: 2321634139
----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------------
| 0 | UPDATE STATEMENT | | 1 | 41 | 679 (1)| 00:00:09 |
| 1 | UPDATE | CS_PERFORMANCE_CURRENT | | | | |
|* 2 | FILTER | | | | | |
| 3 | TABLE ACCESS FULL | CS_PERFORMANCE_CURRENT | 124K| 4968K| 664 (1)| 00:00:08 |
|* 4 | FILTER | | | | | |
| 5 | NESTED LOOPS | | 1 | 52 | 3 (0)| 00:00:01 |
|* 6 | TABLE ACCESS BY INDEX ROWID| CS_TARGET_MODEL_REL | 1 | 26 | 2 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | PK_CS_TARGET_RULE_REL | 1 | | 1 (0)| 00:00:01 |
|* 8 | TABLE ACCESS BY INDEX ROWID| CS_AREA | 1 | 26 | 1 (0)| 00:00:01 |
|* 9 | INDEX UNIQUE SCAN | PK_CS_AREA_NEW | 1 | | 0 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("C"."TARGET_MODE_SEQ_ID"= (SELECT "D"."SEQ_ID" FROM "CS_AREA"
"A","CS_TARGET_MODEL_REL" "D" WHERE :B1=TO_DATE(' 2011-08-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss')
AND "D"."SEQ_ID"=:B2 AND "D"."STAFF_ID"=8 AND "D"."ASSESS_ID"=1265 AND "D"."TARGET_MODEL_ID"=332
AND "D"."STATE"='2' AND "D"."AREA_ID"="A"."AREA_ID" AND "A"."AREA_NAME"='永兴支局'))
4 - filter(:B1=TO_DATE(' 2011-08-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
6 - filter("D"."STAFF_ID"=8 AND "D"."ASSESS_ID"=1265 AND "D"."TARGET_MODEL_ID"=332 AND
"D"."STATE"='2')
7 - access("D"."SEQ_ID"=:B1)
8 - filter("A"."AREA_NAME"='永兴支局')
9 - access("D"."AREA_ID"="A"."AREA_ID")
已用时间: 00: 00: 00.29
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
32670 consistent gets
21 physical reads
0 redo size
536 bytes sent via SQL*Net to client
978 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
0 rows processedUPDATE /*+ PUSH_SUBQ(@D) */CS_PERFORMANCE_CURRENT C
SET C.PERFORMANCE_SCORE = '0.00', C.ASSESS_DESC = '劳动纪律考核'
WHERE C.TARGET_MODE_SEQ_ID =
(SELECT /*+ QB_NAME(D) */ D.SEQ_ID
FROM CS_TARGET_MODEL_REL D, CS_AREA A
WHERE D.ASSESS_ID = 1265
AND C.TARGET_MODE_SEQ_ID = D.SEQ_ID
AND D.STAFF_ID = 8
AND C.COM_DATE = TO_DATE('20110801','YYYYMMDD')
AND D.TARGET_MODEL_ID = 332
AND D.STATE = TO_CHAR(2)
AND D.AREA_ID = A.AREA_ID
AND A.AREA_NAME = '永兴支局')
Plan hash value: 4189652906
----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------------
| 0 | UPDATE STATEMENT | | 1 | 39 | 43 (0)| 00:00:01 |
| 1 | UPDATE | CS_PERFORMANCE_CURRENT | | | | |
|* 2 | TABLE ACCESS FULL | CS_PERFORMANCE_CURRENT | 1 | 39 | 40 (0)| 00:00:01 |
|* 3 | FILTER | | | | | |
| 4 | NESTED LOOPS | | 1 | 47 | 3 (0)| 00:00:01 |
|* 5 | TABLE ACCESS BY INDEX ROWID| CS_TARGET_MODEL_REL | 1 | 25 | 2 (0)| 00:00:01 |
|* 6 | INDEX UNIQUE SCAN | PK_CS_TARGET_RULE_REL | 1 | | 1 (0)| 00:00:01 |
|* 7 | TABLE ACCESS BY INDEX ROWID| CS_AREA | 1 | 22 | 1 (0)| 00:00:01 |
|* 8 | INDEX UNIQUE SCAN | PK_CS_AREA_NEW | 1 | | 0 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("C"."TARGET_MODE_SEQ_ID"= (SELECT /*+ PUSH_SUBQ QB_NAME ("D") */ "D"."SEQ_ID" FROM
"CS_AREA" "A","CS_TARGET_MODEL_REL" "D" WHERE :B1=TO_DATE(' 2011-08-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "D"."SEQ_ID"=:B2 AND "D"."ASSESS_ID"=1265 AND "D"."STAFF_ID"=8 AND
"D"."TARGET_MODEL_ID"=332 AND "D"."STATE"='2' AND "D"."AREA_ID"="A"."AREA_ID" AND
"A"."AREA_NAME"='永兴支局'))
3 - filter(:B1=TO_DATE(' 2011-08-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
5 - filter("D"."ASSESS_ID"=1265 AND "D"."STAFF_ID"=8 AND "D"."TARGET_MODEL_ID"=332 AND
"D"."STATE"='2')
6 - access("D"."SEQ_ID"=:B1)
7 - filter("A"."AREA_NAME"='永兴支局')
8 - access("D"."AREA_ID"="A"."AREA_ID")
统计信息
----------------------------------------------------------
1 recursive calls
0 db block gets
32670 consistent gets
21 physical reads
0 redo size
536 bytes sent via SQL*Net to client
978 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
0 rows processed
可以看到，逻辑读都是一样的，那么这个SQL，加不加HINT性能都一样。其实对于Oracle中的update 语句，如果SQL很复杂，需要关联多个表去做update，这个时候应该用
merge 语句代替 update，用Merge 改写之后 ：
MERGE INTO CS_PERFORMANCE_CURRENT A
USING (SELECT D.SEQ_ID
FROM CS_TARGET_MODEL_REL D,
CS_AREA M
WHERE D.ASSESS_ID = 1265 AND
D.STAFF_ID = 8 AND
D.TARGET_MODEL_ID = 332 AND
D.STATE = TO_CHAR(2) AND
D.AREA_ID = M.AREA_ID AND
M.AREA_NAME = '永兴支局') H
ON (A.TARGET_MODE_SEQ_ID = H.SEQ_ID)
WHEN MATCHED THEN
UPDATE SET A.PERFORMANCE_SCORE = '0.00', A.ASSESS_DESC = '劳动纪律考核' WHERE A.COM_DATE = TO_DATE('20110801', 'YYYYMMDD')；
----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------------
| 0 | MERGE STATEMENT | | 1 | 167 | 750 (1)| 00:00:10 |
| 1 | MERGE | CS_PERFORMANCE_CURRENT | | | | |
| 2 | VIEW | | | | | |
|* 3 | HASH JOIN | | 1 | 210 | 750 (1)| 00:00:10 |
| 4 | NESTED LOOPS | | 1 | 52 | 85 (2)| 00:00:02 |
|* 5 | TABLE ACCESS FULL | CS_TARGET_MODEL_REL | 1 | 26 | 84 (2)| 00:00:02 |
|* 6 | TABLE ACCESS BY INDEX ROWID| CS_AREA | 1 | 26 | 1 (0)| 00:00:01 |
|* 7 | INDEX UNIQUE SCAN | PK_CS_AREA_NEW | 1 | | 0 (0)| 00:00:01 |
| 8 | TABLE ACCESS FULL | CS_PERFORMANCE_CURRENT | 124K| 18M| 664 (1)| 00:00:08 |
----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("A"."TARGET_MODE_SEQ_ID"="D"."SEQ_ID")
5 - filter("D"."STAFF_ID"=8 AND "D"."ASSESS_ID"=1265 AND "D"."TARGET_MODEL_ID"=332 AND
"D"."STATE"='2')
6 - filter("M"."AREA_NAME"='永兴支局')
7 - access("D"."AREA_ID"="M"."AREA_ID")
统计信息
----------------------------------------------------------
333 recursive calls
0 db block gets
3474 consistent gets
3 physical reads
0 redo size
546 bytes sent via SQL*Net to client
998 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
15 sorts (memory)
0 sorts (disk)
0 rows processed
逻辑读下降了近10倍，这里 CS_PERFORMANCE_CURRENT 是全表扫描，它有100W的数据量，所以建立索引在TARGET_MODE_SEQ_ID列上
Plan hash value: 3908453434
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------------
| 0 | MERGE STATEMENT | | 1 | 167 | 88 (2)| 00:00:02 |
| 1 | MERGE | CS_PERFORMANCE_CURRENT | | | | |
| 2 | VIEW | | | | | |
| 3 | TABLE ACCESS BY INDEX ROWID | CS_PERFORMANCE_CURRENT | 1 | 158 | 3 (0)| 00:00:01 |
| 4 | NESTED LOOPS | | 1 | 210 | 88 (2)| 00:00:02 |
| 5 | NESTED LOOPS | | 1 | 52 | 85 (2)| 00:00:02 |
|* 6 | TABLE ACCESS FULL | CS_TARGET_MODEL_REL | 1 | 26 | 84 (2)| 00:00:02 |
|* 7 | TABLE ACCESS BY INDEX ROWID| CS_AREA | 1 | 26 | 1 (0)| 00:00:01 |
|* 8 | INDEX UNIQUE SCAN | PK_CS_AREA_NEW | 1 | | 0 (0)| 00:00:01 |
|* 9 | INDEX RANGE SCAN | IDX_CS_PFC_CURRENT | 1 | | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - filter("D"."STAFF_ID"=8 AND "D"."ASSESS_ID"=1265 AND "D"."TARGET_MODEL_ID"=332 AND
"D"."STATE"='2')
7 - filter("M"."AREA_NAME"='永兴支局')
8 - access("D"."AREA_ID"="M"."AREA_ID")
9 - access("A"."TARGET_MODE_SEQ_ID"="D"."SEQ_ID")
已用时间: 00: 00: 00.18
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
386 consistent gets
0 physical reads
0 redo size
544 bytes sent via SQL*Net to client
998 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
0 rows processed
现在逻辑读降低到386
在Oracle当中，强烈建议 =使用 merge 代替 update语句