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大家好:)我有兩個表，每個表大約有三千萬行，而且我正在尋求在執行計數時提高性能。在Oracle中使用JOIN優化SELECT中的計數
下面是該查詢：
SELECT count(*)
FROM VEHICULE v
JOIN CLIENT c ON c.CL_ID = v.VE_CL_ID
WHERE v.VE_BRAND = 'MITSUBISHI'
AND c.CL_COUNTRY = 'SPAIN';
外鍵在VEHICULE表聲明
CONSTRAINT "VEHICULE_CLIENT_FK" FOREIGN KEY ("VE_CL_ID")
REFERENCES "MY_SCHEMA"."CLIENT" ("CL_ID") ENABLE
而且有外鍵索引：
CREATE INDEX "MY_SCHEMA"."VEHICULE_INDEX_CLIENT" ON "MY_SCHEMA"."VEHICULE" ("CL_ID")
有也是用於搜索條件的列上的索引。
請求最多可能需要40秒。我已經看過位圖連接索引，但我不知道它是否會有所幫助，因爲位圖連接應該是for columns with low cardinalities。這是連接索引的唯一類型嗎？我完全不知如何改善表現。
編輯：
下面是SQL Developer就會顯示（執行計劃）的SQL調優顧問 這個查詢的SQL是沒有AND c.CL_COUNTRY = 'SPAIN'
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : staName9168
Tuning Task Owner : USER
Tuning Task ID : 12125
Scope : COMPREHENSIVE
Time Limit(seconds): 1800
Completion Status : COMPLETED
Started at : 04/23/2013 15:44:35
Completed at : 04/23/2013 15:44:36
-------------------------------------------------------------------------------
There are no recommendations to improve the statement.
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------
1- Original
-----------
Plan hash value: 3808155432
------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 21 | 54011 (1)| 00:10:49 | | | |
| 1 | SORT AGGREGATE | | 1 | 21 | | | | | |
| 2 | PX COORDINATOR | | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10001 | 1 | 21 | | | Q1,01 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | 21 | | | Q1,01 | PCWP | |
|* 5 | HASH JOIN | | 475K| 9745K| 54011 (1)| 00:10:49 | Q1,01 | PCWP | |
| 6 | BUFFER SORT | | | | | | Q1,01 | PCWC | |
| 7 | PX RECEIVE | | 475K| 6497K| 32813 (1)| 00:06:34 | Q1,01 | PCWP | |
| 8 | PX SEND BROADCAST | :TQ10000 | 475K| 6497K| 32813 (1)| 00:06:34 | | S->P | BROADCAST |
|* 9 | TABLE ACCESS BY INDEX ROWID| VEHICULE | 475K| 6497K| 32813 (1)| 00:06:34 | | | |
|* 10 | INDEX RANGE SCAN | VEHICULE_INDEX_BRAND | 616K| | 1621 (2)| 00:00:20 | | | |
| 11 | PX BLOCK ITERATOR | | 20M| 138M| 21146 (1)| 00:04:14 | Q1,01 | PCWC | |
| 12 | TABLE ACCESS FULL | CLIENT | 20M| 138M| 21146 (1)| 00:04:14 | Q1,01 | PCWP | |
------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name/Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$58A6D7F6
9 - SEL$58A6D7F6/[email protected]$1
10 - SEL$58A6D7F6/[email protected]$1
12 - SEL$58A6D7F6/[email protected]$1
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("VE_CL_ID"="CL_ID")
9 - filter("VE_CL_ID" IS NOT NULL)
10 - access("VEHICULE"."VE_BRAND"='MITSUBISHI')
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - (#keys=0) COUNT()[22]
2 - SYS_OP_MSR()[10]
3 - (#keys=0) SYS_OP_MSR()[10]
4 - (#keys=0) SYS_OP_MSR()[10]
5 - (#keys=1)
6 - (#keys=0) "VE_CL_ID"[NUMBER,22]
7 - "VE_CL_ID"[NUMBER,22]
8 - (#keys=0) "VE_CL_ID"[NUMBER,22]
9 - "VE_CL_ID"[NUMBER,22]
10 - "VEHICULE".ROWID[ROWID,10]
11 - "CL_ID"[NUMBER,22]
12 - "CL_ID"[NUMBER,22]
-------------------------------------------------------------------------------
執行計劃顯示什麼？ 「ve_brand」或「cl_country」上是否有索引，如果有的話，它們的選擇性以及它們選擇用於每個表的索引是多少？ – 2013-04-23 13:42:50
你需要在你的'客戶端'表上的索引，參見。解釋計劃的編號12。 – collapsar 2013-04-23 13:56:37
@AlexPoole've_brand'和'cl_country'被編入索引。我會說他們代表每個5％的列。執行計劃始終顯示搜索條件的「INDEX RANGE SCAN」。 （執行計劃包含在編輯中）。單獨的每個表上的SELECT查詢速度非常快，但連接會降低性能。 – BenoitParis 2013-04-23 13:57:15