我需要帮助强制Oracle始终使用表“r_rapport”（~60k行）上的索引行id进行表访问，以便随后避免对“r_attributfeld”（~8m行）进行全表扫描。我有一个查询导致以下计划：
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| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 101 | 22220 | | 63518 (2)| 00:12:43 |
|* 1 | COUNT STOPKEY | | | | | | |
| 2 | VIEW | | 2870 | 616K| | 63518 (2)| 00:12:43 |
|* 3 | SORT ORDER BY STOPKEY | | 2870 | 313K| 696K| 63518 (2)| 00:12:43 |
|* 4 | FILTER | | | | | | |
|* 5 | HASH JOIN SEMI | | 2871 | 314K| | 51920 (2)| 00:10:24 |
|* 6 | HASH JOIN RIGHT SEMI | | 2871 | 299K| | 26084 (2)| 00:05:14 |
| 7 | VIEW | VW_NSO_1 | 214 | 1070 | | 5 (20)| 00:00:01 |
|* 8 | HASH JOIN | | 214 | 5350 | | 5 (20)| 00:00:01 |
|* 9 | INDEX RANGE SCAN | TEST7 | 141 | 1269 | | 2 (0)| 00:00:01 |
|* 10 | INDEX RANGE SCAN | TEST8 | 228 | 3648 | | 2 (0)| 00:00:01 |
|* 11 | HASH JOIN SEMI | | 5848 | 582K| | 26079 (2)| 00:05:13 |
|* 12 | HASH JOIN | | 6547 | 620K| | 243 (2)| 00:00:03 |
|* 13 | INDEX RANGE SCAN | TEST5 | 47 | 470 | | 2 (0)| 00:00:01 |
| 14 | TABLE ACCESS FULL | R_RAPPORT | 60730 | 5159K| | 240 (1)| 00:00:03 |
| 15 | VIEW | VW_SQ_3 | 334K| 1633K| | 25834 (2)| 00:05:11 |
|* 16 | HASH JOIN | | 334K| 14M| 10M| 25834 (2)| 00:05:11 |
| 17 | INDEX FAST FULL SCAN | TEST4 | 476K| 4656K| | 368 (2)| 00:00:05 |
|* 18 | HASH JOIN | | 343K| 11M| 11M| 24214 (2)| 00:04:51 |
|* 19 | TABLE ACCESS FULL | R_ATTRIBUTFELD | 343K| 7722K| | 20483 (2)| 00:04:06 |
| 20 | INDEX FAST FULL SCAN| TEST3 | 1670K| 17M| | 1324 (1)| 00:00:16 |
| 21 | VIEW | VW_SQ_2 | 334K| 1633K| | 25834 (2)| 00:05:11 |
|* 22 | HASH JOIN | | 334K| 14M| 10M| 25834 (2)| 00:05:11 |
| 23 | INDEX FAST FULL SCAN | TEST4 | 476K| 4656K| | 368 (2)| 00:00:05 |
|* 24 | HASH JOIN | | 343K| 11M| 11M| 24214 (2)| 00:04:51 |
|* 25 | TABLE ACCESS FULL | R_ATTRIBUTFELD | 343K| 7722K| | 20483 (2)| 00:04:06 |
| 26 | INDEX FAST FULL SCAN | TEST3 | 1670K| 17M| | 1324 (1)| 00:00:16 |
|* 27 | INDEX RANGE SCAN | TEST6 | 1 | 8 | | 8 (0)| 00:00:01 |
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通过添加FIRST_ROWS（1）提示，这会更改为更理想的计划：
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 1 | 220 | 96 (0)| 00:00:02 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | VIEW | | 1 | 220 | 96 (0)| 00:00:02 |
|* 3 | FILTER | | | | | |
| 4 | NESTED LOOPS | | 1 | 97 | 16 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID | R_RAPPORT | 60730 | 5159K| 6 (0)| 00:00:01 |
| 6 | INDEX FULL SCAN DESCENDING | IDX_R_RAPPORT_3 | 10 | | 2 (0)| 00:00:01 |
|* 7 | INDEX RANGE SCAN | TEST5 | 1 | 10 | 1 (0)| 00:00:01 |
| 8 | NESTED LOOPS | | 1 | 25 | 2 (0)| 00:00:01 |
|* 9 | INDEX RANGE SCAN | TEST7 | 141 | 1269 | 2 (0)| 00:00:01 |
|* 10 | INDEX UNIQUE SCAN | TEST8 | 1 | 16 | 0 (0)| 00:00:01 |
|* 11 | TABLE ACCESS BY INDEX ROWID | R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 12 | NESTED LOOPS | | 2 | 88 | 35 (0)| 00:00:01 |
| 13 | NESTED LOOPS | | 10 | 210 | 7 (0)| 00:00:01 |
|* 14 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 15 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 17 | TABLE ACCESS BY INDEX ROWID| R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 18 | NESTED LOOPS | | 2 | 88 | 35 (0)| 00:00:01 |
| 19 | NESTED LOOPS | | 10 | 210 | 7 (0)| 00:00:01 |
|* 20 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 21 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 22 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 23 | INDEX RANGE SCAN | TEST6 | 1 | 8 | 8 (0)| 00:00:01 |
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不幸的是，这个查询是在运行时编写的，如果这里有三个子请求而不是两个子请求，它将忽略FIRST_ROWS提示并再次对800万行进行多次全表扫描。使用给定的数据分发，rowid的访问速度总是更快（几乎是即时的），而Oracle计划优先考虑几秒钟。
我尝试在两个表上使用ROWID提示，然后才发现它们已被弃用。
任何指针都将受到赞赏。
=编辑=
USE_NL＆amp;新指数
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 101 | 22220 | 3994 (1)| 00:00:48 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | VIEW | | 102 | 22440 | 3994 (1)| 00:00:48 |
| 3 | NESTED LOOPS SEMI | | 1 | 102 | 16 (7)| 00:00:01 |
| 4 | NESTED LOOPS | | 1 | 97 | 11 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID | R_RAPPORT | 58985 | 5011K| 10 (0)| 00:00:01 |
|* 6 | INDEX FULL SCAN DESCENDING | TEST12 | 1 | | 9 (0)| 00:00:01 |
|* 7 | TABLE ACCESS BY INDEX ROWID | R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 8 | NESTED LOOPS | | 2 | 88 | 35 (0)| 00:00:01 |
| 9 | NESTED LOOPS | | 10 | 210 | 7 (0)| 00:00:01 |
|* 10 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 11 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 12 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 13 | TABLE ACCESS BY INDEX ROWID| R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 14 | NESTED LOOPS | | 2 | 88 | 35 (0)| 00:00:01 |
| 15 | NESTED LOOPS | | 10 | 210 | 7 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 17 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 18 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 19 | INDEX RANGE SCAN | TEST6 | 1 | 8 | 8 (0)| 00:00:01 |
|* 20 | INDEX RANGE SCAN | TEST5 | 1 | 10 | 1 (0)| 00:00:01 |
|* 21 | VIEW | VW_NSO_1 | 105 | 525 | 5 (20)| 00:00:01 |
|* 22 | HASH JOIN | | 214 | 5350 | 5 (20)| 00:00:01 |
|* 23 | INDEX RANGE SCAN | TEST7 | 141 | 1269 | 2 (0)| 00:00:01 |
|* 24 | INDEX RANGE SCAN | TEST8 | 228 | 3648 | 2 (0)| 00:00:01 |
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SQL：
select /*+ FIRST_ROWS */ * from (
select *
from r_rapport a
where rb_id in (
select obj_id from obj_recht where obj_typ = 20 and obj_pid = 10065 and maske_id in (
select distinct maske_id
from obj_rechtmaske
where subj_pid = 10065
) )
and rb_id in (
select id from rb_buch where pid = 10065
)
and exists (
select /*+ USE_NL( c d ) */ 1
from r_teilanlage b, r_attribut c, r_attributfeld d
where a.id = b.r_id
and b.id = c.r_teilanlage_id
and c.id = d.r_attribut_id
and d.attributfeld_typ not in ( 20, 25, 40, 78, 79, 90, 92, 123, 124, 125, 126, 127 )
and lower( d.wert ) like lower( '%ä%' )
)
and exists (
select /*+ USE_NL( c d ) */ 1
from r_teilanlage b, r_attribut c, r_attributfeld d
where a.id = b.r_id
and b.id = c.r_teilanlage_id
and c.id = d.r_attribut_id
and d.attributfeld_typ not in ( 20, 25, 40, 78, 79, 90, 92, 123, 124, 125, 126, 127 )
and lower( d.wert ) like lower( '%ö%' )
)
and exists (
select /*+ USE_NL( c d ) */ 1
from r_teilanlage b, r_attribut c, r_attributfeld d
where a.id = b.r_id
and b.id = c.r_teilanlage_id
and c.id = d.r_attribut_id
and d.attributfeld_typ not in ( 20, 25, 40, 78, 79, 90, 92, 123, 124, 125, 126, 127 )
and lower( d.wert ) like lower( '%ä%' )
)
and exists (
select /*+ USE_NL( c d ) */ 1
from r_teilanlage b, r_attribut c, r_attributfeld d
where a.id = b.r_id
and b.id = c.r_teilanlage_id
and c.id = d.r_attribut_id
and d.attributfeld_typ not in ( 20, 25, 40, 78, 79, 90, 92, 123, 124, 125, 126, 127 )
and lower( d.wert ) like lower( '%ö%' )
)
and a.id not in (
select r_id from r_gelesen where ma_id = 144
)
order by a.open_stamp desc
) where rownum <= 101;
及其计划：
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 1 | 220 | 1195K (1)| 03:59:08 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | VIEW | | 1 | 220 | 1195K (1)| 03:59:08 |
|* 3 | FILTER | | | | | |
| 4 | NESTED LOOPS SEMI | | 3213 | 320K| 1018K (1)| 03:23:47 |
| 5 | NESTED LOOPS | | 6547 | 620K| 82249 (1)| 00:16:27 |
| 6 | TABLE ACCESS BY INDEX ROWID | R_RAPPORT | 60730 | 5159K| 21493 (1)| 00:04:18 |
| 7 | INDEX FULL SCAN DESCENDING | IDX_R_RAPPORT_3 | 60730 | | 152 (1)| 00:00:02 |
|* 8 | INDEX RANGE SCAN | TEST5 | 1 | 10 | 1 (0)| 00:00:01 |
|* 9 | VIEW | VW_NSO_1 | 105 | 525 | 143 (0)| 00:00:02 |
| 10 | NESTED LOOPS | | 214 | 5350 | 143 (0)| 00:00:02 |
|* 11 | INDEX RANGE SCAN | TEST7 | 141 | 1269 | 2 (0)| 00:00:01 |
|* 12 | INDEX RANGE SCAN | TEST8 | 2 | 32 | 1 (0)| 00:00:01 |
|* 13 | TABLE ACCESS BY INDEX ROWID | R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 14 | NESTED LOOPS | | 6 | 264 | 97 (0)| 00:00:02 |
| 15 | NESTED LOOPS | | 30 | 630 | 13 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 17 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 18 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 19 | TABLE ACCESS BY INDEX ROWID | R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 20 | NESTED LOOPS | | 6 | 264 | 97 (0)| 00:00:02 |
| 21 | NESTED LOOPS | | 30 | 630 | 13 (0)| 00:00:01 |
|* 22 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 23 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 24 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 25 | TABLE ACCESS BY INDEX ROWID | R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 26 | NESTED LOOPS | | 6 | 264 | 97 (0)| 00:00:02 |
| 27 | NESTED LOOPS | | 30 | 630 | 13 (0)| 00:00:01 |
|* 28 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 29 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 30 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 31 | TABLE ACCESS BY INDEX ROWID| R_ATTRIBUTFELD | 1 | 23 | 3 (0)| 00:00:01 |
| 32 | NESTED LOOPS | | 6 | 264 | 97 (0)| 00:00:02 |
| 33 | NESTED LOOPS | | 30 | 630 | 13 (0)| 00:00:01 |
|* 34 | INDEX RANGE SCAN | TEST4 | 9 | 90 | 3 (0)| 00:00:01 |
|* 35 | INDEX RANGE SCAN | TEST3 | 3 | 33 | 2 (0)| 00:00:01 |
|* 36 | INDEX RANGE SCAN | IDX_R_ATTRIBUTFELD_1 | 6 | | 2 (0)| 00:00:01 |
|* 37 | INDEX RANGE SCAN | TEST6 | 1 | 8 | 8 (0)| 00:00:01 |
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这个查询立即完成，这是一个可怕的，可怕的成本估算。
答案 0 :(得分：1)
如果你想避免在r_attributfeld上完全访问表，你应该在这个表上尝试一个嵌套循环。 如果Oracle“不理解”你想要的东西，也许你必须有一个领先的（r_rapport r_attributfeld）（或有序的提示）
答案 1 :(得分：-1)
并不总是你认为更好的计划是更好的计划。快速返回第一行是使用嵌套循环和rowid访问的正确方法。但是如果你想快速返回所有结果集，即使你通过rowid加入也是更有效的（“select * from tabid in rowid in（...）”或“... join tab tab.rowid” = ...'）。所以我认为甲骨文为你挑选了正确的计划。