我有一个SQL查询，在连接两个表时速度很慢，但是当我第一次查询一个表并且输出查询另一个表时速度很快。
环境/先决条件
Oracle版：
Oracle Database 11g企业版11.2.0.3.0版 - 64位生产
涉及的对象：
cfc_materialized（物化视图，21,5 Mio行）
联系（表，12,6 Mio行）
涉及的指数：
联系上创建索引CONTACT_CLIENT（客户）;
CREATE INDEX CFC_MATERIALIZED_A_S_T ON CFC_MATERIALIZED（ASSOCIATION_TYPE，SOURCEID，TARGETID）;
我已经用cascade =＆gt;重新计算了2个表的统计数据真：
BEGIN
SYS.DBMS_STATS.GATHER_TABLE_STATS (
OwnName => '...'
,TabName => '...'
,Estimate_Percent => 0
,Degree => 4
,Cascade => TRUE
,No_Invalidate => FALSE);
END;
/
问题
我有以下查询：
SELECT c.*
FROM contact c
WHERE c.client in (
SELECT cfc.targetid
FROM cfc_materialized cfc
WHERE cfc.sourceid = 'e95027f0-a83e-11e3-a0ae-005056aebabc'
AND cfc.association_type = 'ContactDataSharing'
)
AND c.deleted = 0;
解释计划：
--------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 11M| 2214M| 38976 (1)| 00:07:48 | | | |
| 1 | PX COORDINATOR | | | | | | | | |
| 2 | PX SEND QC (RANDOM) | :TQ10001 | | | | | Q1,01 | P->S | QC (RAND) |
| 3 | NESTED LOOPS | | | | | | Q1,01 | PCWP | |
| 4 | NESTED LOOPS | | 11M| 2214M| 38976 (1)| 00:07:48 | Q1,01 | PCWP | |
| 5 | SORT UNIQUE | | 2164 | 196K| 10672 (1)| 00:02:09 | Q1,01 | PCWP | |
| 6 | PX RECEIVE | | 2164 | 196K| 10672 (1)| 00:02:09 | Q1,01 | PCWP | |
| 7 | PX SEND HASH | :TQ10000 | 2164 | 196K| 10672 (1)| 00:02:09 | Q1,00 | P->P | HASH |
| 8 | PX BLOCK ITERATOR | | 2164 | 196K| 10672 (1)| 00:02:09 | Q1,00 | PCWC | |
|* 9 | MAT_VIEW ACCESS FULL | CFC_MATERIALIZED | 2164 | 196K| 10672 (1)| 00:02:09 | Q1,00 | PCWP | |
|* 10 | INDEX RANGE SCAN | CONTACT_CLIENT | 5500 | | 37 (0)| 00:00:01 | Q1,01 | PCWP | |
|* 11 | TABLE ACCESS BY INDEX ROWID| CONTACT | 5474 | 550K| 973 (0)| 00:00:12 | Q1,01 | PCWP | |
--------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
9 - filter("CFC"."SOURCEID"='e95027f0-a83e-11e3-a0ae-005056aebabc' AND "CFC"."ASSOCIATION_TYPE"='ContactDataSharing')
10 - access("C"."CLIENT"="CFC"."TARGETID")
11 - filter("C"."DELETED"=0)enter code here
这需要很长时间，我想知道为什么cfc_materialized有完全访问权限。 当我将查询拆分为2个查询时，速度要快得多。 第一个查询：
SELECT cfc.targetid
FROM cfc_materialized cfc
WHERE cfc.sourceid = 'e95027f0-a83e-11e3-a0ae-005056aebabc'
AND cfc.association_type = 'ContactDataSharing';
此查询返回2个目标。 解释计划：
-------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2164 | 196K| 36 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| CFC_MATERIALIZED_A_S_T | 2164 | 196K| 36 (0)| 00:00:01 |
-------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("CFC"."ASSOCIATION_TYPE"='ContactDataSharing' AND
"CFC"."SOURCEID"='e95027f0-a83e-11e3-a0ae-005056aebabc')
这是第二个查询。我使用第一个查询的输出作为IN参数的输入：
SELECT *
FROM contact c
WHERE c.client in (
'e95027f0-a83e-11e3-a0ae-005056aebabc',
'eb37d3b0-a83e-11e3-a0ae-005056aebabc'
)
AND c.deleted = 0;
解释计划：
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2814 | 283K| 505 (0)| 00:00:07 |
| 1 | INLIST ITERATOR | | | | | |
|* 2 | TABLE ACCESS BY INDEX ROWID| CONTACT | 2814 | 283K| 505 (0)| 00:00:07 |
|* 3 | INDEX RANGE SCAN | CONTACT_CLIENT | 2827 | | 23 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("C"."DELETED"=0)
3 - access("C"."CLIENT"='e95027f0-a83e-11e3-a0ae-005056aebabc' OR
"C"."CLIENT"='eb37d3b0-a83e-11e3-a0ae-005056aebabc')
问题
所以我的问题是，为什么CBO没有以类似的方式执行查询，比如手动执行2个查询？我还尝试使用提示查询以使用与2个查询中相同的索引：
SELECT /*+ index(c CONTACT_CLIENT) */ c.*
FROM contact c
WHERE c.client in (
SELECT /*+ index(cfc CFC_MATERIALIZED_A_S_T) */ cfc.targetid
FROM cfc_materialized cfc
WHERE cfc.sourceid = 'e95027f0-a83e-11e3-a0ae-005056aebabc'
AND cfc.association_type = 'ContactDataSharing'
)
AND c.deleted = 0;
然后我得到一个更糟糕的解释计划：
-------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 11M| 2214M| 305K (1)| 01:01:09 |
| 1 | NESTED LOOPS | | | | | |
| 2 | NESTED LOOPS | | 11M| 2214M| 305K (1)| 01:01:09 |
| 3 | SORT UNIQUE | | 2164 | 196K| 36 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | CFC_MATERIALIZED_A_S_T | 2164 | 196K| 36 (0)| 00:00:01 |
|* 5 | INDEX RANGE SCAN | CONTACT_CLIENT | 5500 | | 37 (0)| 00:00:01 |
|* 6 | TABLE ACCESS BY INDEX ROWID| CONTACT | 5474 | 550K| 973 (0)| 00:00:12 |
-------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("CFC"."ASSOCIATION_TYPE"='ContactDataSharing' AND
"CFC"."SOURCEID"='e95027f0-a83e-11e3-a0ae-005056aebabc')
5 - access("C"."CLIENT"="CFC"."TARGETID")
6 - filter("C"."DELETED"=0)
我也尝试过连接而不是像Alexander和StanislavL建议的IN子句：
SELECT c.*
FROM contact c
JOIN cfc_materialized cfc ON c.client = cfc.targetid
WHERE cfc.sourceid = 'e95027f0-a83e-11e3-a0ae-005056aebabc'
AND cfc.association_type = 'ContactDataSharing'
AND c.deleted = 0;
并得到以下解释计划，这又是非常慢的（比两个单独的查询慢）：
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 11M| 2214M| 51745 (1)| 00:10:21 |
|* 1 | HASH JOIN | | 11M| 2214M| 51745 (1)| 00:10:21 |
|* 2 | INDEX RANGE SCAN | CFC_MATERIALIZED_A_S_T | 2164 | 196K| 36 (0)| 00:00:01 |
|* 3 | TABLE ACCESS FULL| CONTACT | 12M| 1237M| 51649 (1)| 00:10:20 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("C"."CLIENT"="CFC"."TARGETID")
2 - access("CFC"."ASSOCIATION_TYPE"='ContactDataSharing' AND
"CFC"."SOURCEID"='e95027f0-a83e-11e3-a0ae-005056aebabc')
3 - filter("C"."DELETED"=0)
答案 0 :(得分：0)
SELECT c.*
FROM contact c
join (
SELECT cfc.targetid as client
FROM cfc_materialized cfc
WHERE cfc.sourceid = 'e95027f0-a83e-11e3-a0ae-005056aebabc'
AND cfc.association_type = 'ContactDataSharing'
) sub ON c.client=sub.client
AND c.deleted = 0;
使用加入而不是IN来避免为WHERE中的每一行计算相同的查询
答案 1 :(得分：0)
主要是，避免Contact表上的完整表访问。
避免c.*，指定具体的列列表。
重建索引
CREATE INDEX CFC_MATERIALIZED_A_S_T ON CFC_MATERIALIZED(TARGETID, ASSOCIATION_TYPE, SOURCEID);
控制加入订单访问。
让我知道。