我终于问了我的第一个问题（尽管我是一个长期的跟踪者）。
前几天在工作中，一个 SQL 查询引起了我的注意。问题是WHERE子句中的性能，当使用IN运算符将索引与可能的值进行比较时。
SELECT SUM (parts.quantity) AS quantity,
concessions.concessionCode,
concessions.description AS concessionDesc,
parts.type,
activities.activityCode,
REPLACE (activities.activityCode, activities.lvl2 || '-', '') AS activityCodeDisplay,
strings.activityDesc,
strings.activityDesc2,
strings.activityDesc3
FROM tb_parts parts,
tb_activities activities,
tb_strings strings,
tb_concessions concessions
WHERE parts.activityCode = activities.activityCode
AND parts.concessionCode = activities.concessionCode
AND activities.concessionCode = concesions.concessionCode
AND activities.concessionCode = strings.concessionCode
AND activities.activityCode = strings.activityCode
AND strings.language = 'ENG'
--AND parts.concesionCode IN ('ZD', 'G9', 'TR', 'JS0')
AND parts.concesionCode IN ('ZD', 'G9')
AND parts.date >= TO_DATE ('01/01/2013 00:00:00', 'DD/MM/YYYY HH24:MI:SS')
AND parts.date <= TO_DATE ('30/04/2013 23:59:59', 'DD/MM/YYYY HH24:MI:SS')
AND parts.type IN ('U', 'M')
AND parts.value = 'E'
GROUP BY concesions.concessionCode,
concesions.description,
parts.type,
activities.activityCode,
REPLACE (activities.activityCode, activities.lvl2|| '-', ''),
strings.activityDesc,
strings.activityDesc2,
strings.activityDesc3
ORDER BY concesions.concessionCode;
我遇到的问题是这样的 - 如果查询按原样运行（有两个值IN），则需要 30 秒。如果它使用四个值运行（就像在注释行中一样），则查询需要 5 秒。我希望将索引与多个值进行比较需要更多时间，但似乎并非如此。我在白天重复了几次“测试”，它们总是或多或少相同（30 +-1s，5 +-1s）。
任何关于为什么会以这种方式表现的见解都将不胜感激！
PS 我已经翻译了表格/列的名称，如果有任何差异，我很抱歉。
PPS我已经用joins重写了这段代码，它更快，但是这个异常背后的原因仍然困扰着我:)
编辑：终于上班了！经过一番修改，我已经能够为这两个版本创建执行计划，甚至为第三个版本的查询（在4 和 2 中都有值where，时间约为 600 毫秒）。另外，关于表格中的数据有几个问题，所以这里有一些信息：
All the stats are analyzed the day that queries were executed
Table parts
total rows - 3.2 M
matches for 2 values - 1.08 M (~34%)
matches for 4 values - 1.30 M (~41%)
Table activities
total rows - 3866
matches for 2 values - 321 (~ 8%)
matches for 4 values - 644 (~16%)
Table strings
total rows - 7436
matches for 2 values - 642 (~ 8%)
matches for 4 values - 1288 (~17%)
Index in_parts
codConcession
username
date
正因为如此，我认为在使用动态采样时（除了 +2/3s 之外）没有大的区别（如果我做得正确，也就是/*+ dynamic_sampling(tb_parts 10) */在SELECT关键字之后）
对于两个值：
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 186 | 864 (1)| 00:00:11 |
| 1 | SORT ORDER BY | | 1 | 186 | 864 (1)| 00:00:11 |
| 2 | HASH GROUP BY | | 1 | 186 | 864 (1)| 00:00:11 |
|* 3 | TABLE ACCESS BY INDEX ROWID | tb_parts | 1 | 37 | 818 (1)| 00:00:10 |
| 4 | NESTED LOOPS | | 1 | 186 | 862 (1)| 00:00:11 |
| 5 | NESTED LOOPS | | 1 | 149 | 44 (0)| 00:00:01 |
| 6 | NESTED LOOPS | | 34 | 2108 | 10 (0)| 00:00:01 |
| 7 | INLIST ITERATOR | | | | | |
| 8 | TABLE ACCESS BY INDEX ROWID| tb_concesions | 2 | 54 | 2 (0)| 00:00:01 |
|* 9 | INDEX UNIQUE SCAN | pk_concession | 2 | | 1 (0)| 00:00:01 |
| 10 | TABLE ACCESS BY INDEX ROWID | tb_activities | 17 | 595 | 4 (0)| 00:00:01 |
|* 11 | INDEX RANGE SCAN | pk_activity | 17 | | 2 (0)| 00:00:01 |
| 12 | TABLE ACCESS BY INDEX ROWID | tb_strings | 1 | 87 | 1 (0)| 00:00:01 |
|* 13 | INDEX UNIQUE SCAN | pk_string | 1 | | 0 (0)| 00:00:01 |
|* 14 | INDEX RANGE SCAN | in_parts | 454 | | 648 (1)| 00:00:08 |
-----------------------------------------------------------------------------------------------------
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("parts"."value"='E'
AND ("parts"."type"='M' OR "parts"."type"='U')
AND "parts"."activityCode"="activities"."activityCode")
9 - access("concessions"."concessionCode"='G9'
OR "concessions"."concessionCode"='ZD')
11 - access("activities"."concessionCode"="concessions"."concessionCode")
filter("activities"."concessionCode"='G9'
OR "activities"."concessionCode"='ZD')
13 - access("activities"."concessionCode"="strings"."concessionCode"
AND "activities"."activityCode"="strings"."activityCode"
AND "strings"."language"='ENG')
filter("strings"."concessionCode"='G9'
OR "strings"."concessionCode"='ZD')
14 - access("parts"."concessionCode"="activities"."concessionCode"
AND "parts"."date">=TO_DATE('2013-01-01 00:00:00',
'syyyy-mm-dd hh24:mi:ss')
AND "parts"."date"<=TO_DATE(' 2013-04-30 23:59:59',
'syyyy-mm-dd hh24:mi:ss'))
filter("parts"."date">=TO_DATE('2013-01-01 00:00:00',
'syyyy-mm-dd hh24:mi:ss')
AND ("parts"."concessionCode"='G9'
OR "parts"."concessionCode"='ZD')
AND "parts"."date"<=TO_DATE(' 2013-04-30 23:59:59',
'syyyy-mm-dd hh24:mi:ss'))
对于四个值：
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 186 | 7412 (2)| 00:01:29 |
| 1 | SORT ORDER BY | | 1 | 186 | 7412 (2)| 00:01:29 |
| 2 | HASH GROUP BY | | 1 | 186 | 7412 (2)| 00:01:29 |
| 3 | NESTED LOOPS | | 1 | 186 | 7410 (2)| 00:01:29 |
|* 4 | HASH JOIN | | 17 | 1683 | 7393 (2)| 00:01:29 |
|* 5 | HASH JOIN | | 136 | 8432 | 21 (5)| 00:00:01 |
| 7 | TABLE ACCESS BY INDEX ROWID| tb_concesions | 4 | 108 | 2 (0)| 00:00:01 |
|* 8 | INDEX UNIQUE SCAN | pk_concession | 4 | | 1 (0)| 00:00:01 |
|* 9 | TABLE ACCESS FULL | tb_activities | 644 | 22540 | 18 (0)| 00:00:01 |
|* 10 | TABLE ACCESS FULL | tb_parts | 4310 | 155K| 7372 (2)| 00:01:29 |
| 11 | TABLE ACCESS BY INDEX ROWID | tb_strings | 1 | 87 | 1 (0)| 00:00:01 |
|* 12 | INDEX UNIQUE SCAN | pk_string | 1 | | 0 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
---------------------------------------------------
4 - access("parts"."activityCode"="activities"."activityCode"
AND "parts"."concessionCode"="activities"."concessionCode")
5 - access("activities"."concessionCode"="concessions"."concessionCode")
8 - access("concessions"."concessionCode"='G9'
OR "concessions"."concessionCode"='JS0'
OR "concessions"."concessionCode"='TR'
OR "concessions"."concessionCode"='ZD')
9 - filter("activities"."concessionCode"='G9'
OR "activities"."concessionCode"='JS0'
OR "activities"."concessionCode"='TR'
OR "activities"."concessionCode"='ZD')
10 - filter("parts"."date">=TO_DATE(' 2013-01-01 00:00:00',
'syyyy-mm-dd hh24:mi:ss')
AND "parts"."value"='E'
AND ("parts"."type"='M' OR "parts"."type"='U')
AND ("parts"."concessionCode"='G9'
OR "parts"."concessionCode"='JS0'
OR "parts"."concessionCode"='TR'
OR "parts"."concessionCode"='ZD')
AND "parts"."date"<=TO_DATE(' 2013-04-30 23:59:59',
'syyyy-mm-dd hh24:mi:ss'))
12 - access("activities"."concessionCode"="strings"."concessionCode"
AND "activities"."activityCode"="strings"."activityCode"
AND "strings"."language"='ENG')
filter("strings"."concessionCode"='G9'
OR "strings"."concessionCode"='JS0'
OR "strings"."concessionCode"='TR'
OR "strings"."concessionCode"='ZD')
最后是六个值：
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 186 | 4525 (1)| 00:00:55 |
| 1 | SORT ORDER BY | | 1 | 186 | 4525 (1)| 00:00:55 |
| 2 | HASH GROUP BY | | 1 | 186 | 4525 (1)| 00:00:55 |
| 3 | NESTED LOOPS | | 1 | 186 | 4523 (1)| 00:00:55 |
|* 4 | HASH JOIN | | 9 | 891 | 4514 (1)| 00:00:55 |
|* 5 | HASH JOIN | | 136 | 8432 | 21 (5)| 00:00:01 |
| 6 | INLIST ITERATOR | | | | | |
| 7 | TABLE ACCESS BY INDEX ROWID| tb_concesions | 4 | 108 | 2 (0)| 00:00:01 |
|* 8 | INDEX UNIQUE SCAN | pk_concession | 4 | | 1 (0)| 00:00:01 |
|* 9 | TABLE ACCESS FULL | tb_activities | 644 | 22540 | 18 (0)| 00:00:01 |
| 10 | INLIST ITERATOR | | | | | |
|* 11 | TABLE ACCESS BY INDEX ROWID | tb_parts | 2155 | 79735 | 4493 (1)| 00:00:54 |
|* 12 | INDEX RANGE SCAN | in_parts | 8620 | | 1277 (1)| 00:00:16 |
| 13 | TABLE ACCESS BY INDEX ROWID | tb_strings | 1 | 87 | 1 (0)| 00:00:01 |
|* 14 | INDEX UNIQUE SCAN | pk_string | 1 | | 0 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("parts"."activityCode"="activities"."activityCode"
AND "parts"."concessionCode"="activities"."concessionCode")
5 - access("activities"."concessionCode"="concessions"."concessionCode")
8 - access("concessions"."concessionCode"='G9'
OR "concessions"."concessionCode"='JS0'
OR "concessions"."concessionCode"='TR'
OR "concessions"."concessionCode"='ZD')
9 - filter("activities"."concessionCode"='G9'
OR "activities"."concessionCode"='JS0'
OR "activities"."concessionCode"='TR'
OR "activities"."concessionCode"='ZD')
11 - filter("parts"."value"='E'
AND ("parts"."type"='M' OR "parts"."type"='U'))
12 - access(("parts"."concessionCode"='G9'
OR "parts"."concessionCode"='ZD')
AND "parts"."date">=TO_DATE(' 2013-01-01 00:00:00',
'syyyy-mm-dd hh24:mi:ss')
AND "parts"."date"<=TO_DATE(' 2013-04-30 23:59:59',
'syyyy-mm-dd hh24:mi:ss'))
filter("parts"."date">=TO_DATE(' 2013-01-01 00:00:00',
'syyyy-mm-dd hh24:mi:ss')
AND "parts"."date"<=TO_DATE(' 2013-04-30 23:59:59',
'syyyy-mm-dd hh24:mi:ss'))
14 - access("activities"."concessionCode"="strings"."concessionCode"
AND "activities"."activityCode"="strings"."activityCode"
AND "strings"."language"='ENG')
filter("strings"."concessionCode"='G9'
OR "strings"."concessionCode"='JS0'
OR "strings"."concessionCode"='TR'
OR "strings"."concessionCode"='ZD')
由于这是我第一次与执行计划会面，我只能猜测延迟的原因是什么。在 4 到 6 个值之间，我猜这是从 FULL ACCESS 到 ACCESS BY INDEX 的变化。此外，当访问表格时，四个值的过滤器（id 10）包含所有四个让步值；而对于六个值，两个让步值在访问部分，过滤器只包含日期、类型和值。