我有一个长期运行的Oracle查询,它使用了一系列:
WHERE EXISTS (SELECT NULL FROM Table WHERE TableColumn IN (...))
而不是使用
SELECT NULL
,它通过整个表格来寻找标准,我不能把
FETCH NEXT 1 ROW ONLY
因为我只在乎
TableColumn
是
IN (...)
?
这样地:
WHERE EXISTS (SELECT NULL FROM Table WHERE TableColumn IN (...) FETCH NEXT 1 ROW ONLY)
所以
WHERE EXISTS
会更快评估。
编辑:
下面是不带
FETCH NEXT
所附条款:
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 75 | 521611 | |
| 1 | SORT AGGREGATE | | 1 | 75 | | |
| 2 | HASH JOIN | | 531266 | 39844950 | 521611 | |
| 3 | TABLE ACCESS FULL | ACCT | 47574 | 523314 | 418 | |
| 4 | HASH JOIN | | 531224 | 33998336 | 521185 | |
| 5 | INDEX FAST FULL SCAN | PK_ACTVTYP | 454 | 2270 | 2 | |
| 6 | HASH JOIN | | 531224 | 31342216 | 521177 | |
| 7 | INDEX FULL SCAN | PK_ACTVCAT | 67 | 335 | 1 | |
| 8 | HASH JOIN SEMI | | 531224 | 28686096 | 521169 | |
| 9 | NESTED LOOPS SEMI | | 531224 | 28686096 | 521169 | |
| 10 | STATISTICS COLLECTOR | | | | | |
| 11 | HASH JOIN RIGHT SEMI | | 531224 | 25498752 | 112887 | |
| 12 | TABLE ACCESS FULL | AMSACTVGRPEMPL | 2364 | 35460 | 10 | |
| 13 | TABLE ACCESS FULL | ACTV | 12779986 | 421739538 | 112712 | |
| 14 | INDEX RANGE SCAN | ACTVSUBACTV_DX2 | 163091724 | 978550344 | 251246 | |
| 15 | INDEX FAST FULL SCAN | ACTVSUBACTV_DX2 | 163091724 | 978550344 | 251246 | |
------------------------------------------------------------------------------------------------
下面是带有
接下一个
所附条款:
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 69 | 113148 | |
| 1 | SORT AGGREGATE | | 1 | 69 | | |
| 2 | FILTER | | | | | |
| 3 | HASH JOIN | | 531221 | 36654249 | 113144 | |
| 4 | TABLE ACCESS FULL | ACCT | 47574 | 523314 | 418 | |
| 5 | HASH JOIN | | 531179 | 30808382 | 112718 | |
| 6 | INDEX FAST FULL SCAN | PK_ACTVTYP | 454 | 2270 | 2 | |
| 7 | HASH JOIN | | 531179 | 28152487 | 112710 | |
| 8 | INDEX FULL SCAN | PK_ACTVCAT | 67 | 335 | 1 | |
| 9 | HASH JOIN RIGHT SEMI | | 531179 | 25496592 | 112702 | |
| 10 | TABLE ACCESS FULL | AMSACTVGRPEMPL | 2167 | 32505 | 10 | |
| 11 | TABLE ACCESS FULL | ACTV | 12778893 | 421703469 | 112527 | |
| 12 | VIEW | | 1 | 13 | 4 | |
| 13 | WINDOW BUFFER PUSHED RANK | | 8 | 48 | 4 | |
| 14 | INDEX RANGE SCAN | ACTVSUBACTV_DX2 | 8 | 48 | 4 | |
------------------------------------------------------------------------------------------------
从我看来,它看起来像没有
接下一个
它增加了更多的开销
TABLE ACCESS FULL
编辑#2
添加
AND ROWNUM = 1
而不是
只取下一行
:
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 54 | 128114 | |
| 1 | SORT AGGREGATE | | 1 | 54 | | |
| 2 | FILTER | | | | | |
| 3 | HASH JOIN | | 12779902 | 690114708 | 113296 | |
| 4 | TABLE ACCESS FULL | ACCT | 47574 | 523314 | 418 | |
| 5 | HASH JOIN | | 12778893 | 549492399 | 112713 | |
| 6 | MERGE JOIN CARTESIAN | | 30418 | 304180 | 31 | |
| 7 | INDEX FULL SCAN | PK_ACTVCAT | 67 | 335 | 1 | |
| 8 | BUFFER SORT | | 454 | 2270 | 30 | |
| 9 | INDEX FAST FULL SCAN | PK_ACTVTYP | 454 | 2270 | 0 | |
| 10 | TABLE ACCESS FULL | ACTV | 12778893 | 421703469 | 112517 | |
| 11 | COUNT STOPKEY | | | | | |
| 12 | INLIST ITERATOR | | | | | |
| 13 | INDEX UNIQUE SCAN | PK_AMSACTVGRPEMPL | 1 | 15 | 2 | |
| 14 | COUNT STOPKEY | | | | | |
| 15 | INDEX RANGE SCAN | ACTVSUBACTV_DX2 | 2 | 12 | 4 | |
------------------------------------------------------------------------------------------------
