oracle 謂詞表示式對基數的影響(及11G改進)
簡單的選擇率與函式問題,下面只用col>字面值的 選擇率,計算 比較方便
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> conn xh/a831115
Connected.
SQL> show user
USER is "XH"
SQL> create table t1 (a int);
Table created.
SQL> declare
2 begin
3 for i in 1..10000 loop
4 insert into t1 values(i);
5 end loop;
6 commit;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL> exec dbms_stats.gather_table_stats('XH','T1');
PL/SQL procedure successfully completed.
SQL> select owner,num_rows from dba_tables where table_name='T1'
2 ;
OWNER NUM_ROWS
------------------------------ ----------
XH 10000
SQL> select table_name,density,num_nulls,num_distinct from user_tab_col_statistics where table_name='T1'
2 ;
TABLE_NAME DENSITY NUM_NULLS NUM_DISTINCT
------------------------------ ---------- ---------- ------------
T1 .0001 0 10000
SQL> SQL> select count(*) from t1 where a>2;
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 6 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | TABLE ACCESS FULL| T1 | 9999 | 29997 | 6 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("A">2)
這個選擇率 計算公式為:
分析a>2 是一個無邊 開區間 (所謂無邊界 就是一側沒有邊界)
a>2選擇率=(high_value – limit) / (high_value – low_value )
SQL> select (10000-2)/(10000-1) from dual;
(10000-2)/(10000-1)
-------------------
.99989999
card=num_rows*選擇率
SQL> select 10000*.99989999 from dual;
10000*.99989999
---------------
9998.9999～～～～～～～～～～～～～～～可以看到10gr2是向上舍入(ceil)
最後的card(rows)= num_rows*選擇率=9999 rows
現在使用函式
SQL> select count(*) from t1 where to_char(a,'xx')>'2';
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 7 (15)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | TABLE ACCESS FULL| T1 | 500 | 1500 | 7 (15)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter(TO_CHAR("A",'xx')>'2')
選擇率 是5%(跟使用bind(!=條件) or sql中用like 時選擇率一樣) CARD=NUM_ROW*5%=500
這樣資訊是不準確的 11g對此進行了改善
看下11g情況
11g 提供擴充套件列統計資訊收集(基於表示式or組合列),原理就是為表示式子或一組列建立一個隱藏列,在這個隱藏列上收集資訊.
這個虛擬列並不實際儲存資料,只在執行時根據一個基於其他欄位的表示式生成虛擬列的資訊.(感覺有點象view的意思,無實際內容,節省空間)
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE 11.1.0.6.0 Production
TNS for Linux: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production
SQL> conn xh/a831115
Connected.
SQL> create table t1 (a int);
Table created.
SQL> declare
2 begin
3 for i in 1..10000 loop
4 insert into t1 values(i);
5 end loop;
6 commit;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL> set autotrace trace exp
SQL> select count(*) from t1 where a>2;
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 7 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | TABLE ACCESS FULL| T1 | 9999 | 29997 | 7 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("A">2)
SQL> select count(*) from t1 where to_char(a)>'2';
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 7 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | TABLE ACCESS FULL| T1 | 500 | 1500 | 7 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter(TO_CHAR("A")>'2')
SQL> select dbms_stats.create_extended_stats(ownname=>'XH',tabname=>'T1',extension=>'(to_char(a))') from dual;
DBMS_STATS.CREATE_EXTENDED_STATS(OWNNAME=>'XH',TABNAME=>'T1',EXTENSION=>'(TO_CHA
--------------------------------------------------------------------------------
SYS_STUQ8Q3O$I37YENJXKXE0CSTFF ~~~~~~~~~~~~~~~~~~~~~~~~~~返回這個擴充套件列名(sys_stu開頭)
另外drop_extended_stats可以刪除擴充套件統計資訊(一個procedure)
SQL> desc user_stat_extensions;
Name Null? Type
----------------------------------------- -------- ----------------------------
TABLE_NAME NOT NULL VARCHAR2(30)
EXTENSION_NAME NOT NULL VARCHAR2(30)
EXTENSION CLOB
CREATOR VARCHAR2(6)
DROPPABLE VARCHAR2(3)
SQL> col extension for a40
SQL> select extension_name,extension from user_stat_extensions where table_name='T1';
EXTENSION_NAME EXTENSION
------------------------------ ----------------------------------------
SYS_STUQ8Q3O$I37YENJXKXE0CSTFF (TO_CHAR("A"))
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T1';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ------------------- --- ---------- ------------
SYS_STUQ8Q3O$I37YENJXKXE0CSTFF VARCHAR2 YES TO_CHAR("A
")
A NUMBER NO 10000
]]
SQL> set autotrace trace exp
SQL> select count(*) from t1 where to_char(a)>'2';
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 7 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | TABLE ACCESS FULL| T1 | 500 | 1500 | 7 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("T1"."SYS_STUQ8Q3O$I37YENJXKXE0CSTFF">'2')
SQL> exec dbms_stats.gather_table_stats('XH','T1');
PL/SQL procedure successfully completed.
SQL> set autotrace off
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T1';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ------------------- --- ---------- ------------
SYS_STUQ8Q3O$I37YENJXKXE0CSTFF VARCHAR2 YES TO_CHAR("A 10000 ~~~~~~~~~~~~~~~~~~~~~要重新收集下 統計資訊
")
A NUMBER NO 10000
SQL> set autotrace trace exp
SQL> select count(*) from t1 where to_char(a)>'2';
Execution Plan
----------------------------------------------------------
Plan hash value: 3724264953
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 8 | 7 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 8 | | |
|* 2 | TABLE ACCESS FULL| T1 | 8902 | 71216 | 7 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("T1"."SYS_STUQ8Q3O$I37YENJXKXE0CSTFF">'2')
有改進 但資訊還是不正確,查了下擴充套件列統計資訊基於hash函式(sys_op_combined_hash),所以僅適用與=,(!=)的都不適用無法利用擴充套件統計資訊,不過測試看到還是影響了card且card接近實際值,(也許沒有做足夠做詳細的測試)
看下 =
SQL> show user
USER is "XH"
SQL> create table t2( a varchar2(10));
Table created.
SQL> declare
2 begin
3 for i in 1..1000 loop
4 insert into t2 values('a');
5 end loop;
6 commit;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL> exec dbms_stats.gather_table_stats('XH','T2');
PL/SQL procedure successfully completed.
SQL> set autotrace trace exp
SQL> select * from t2 where a='a';
Execution Plan
----------------------------------------------------------
Plan hash value: 1513984157
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1000 | 2000 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T2 | 1000 | 2000 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("A"='a')
SQL> select * from t2 where upper(a)='A';
Execution Plan
----------------------------------------------------------
Plan hash value: 1513984157
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 10 | 20 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T2 | 10 | 20 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(UPPER("A")='A')
SQL> select dbms_stats.create_extended_stats(ownname=>'XH',tabname=>'T2',extension=>'(upper(a))') from dual;
DBMS_STATS.CREATE_EXTENDED_STATS(OWNNAME=>'XH',TABNAME=>'T2',EXTENSION=>'(UPPER(
--------------------------------------------------------------------------------
SYS_STUWSDP8IKNLLR9QA4XVKCO0BY
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T2';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ------------------- --- ---------- ------------
SYS_STUWSDP8IKNLLR9QA4XVKCO0BY VARCHAR2 YES UPPER("A")
A VARCHAR2 NO 1
SQL> exec dbms_stats.gather_table_stats('XH','T2');
PL/SQL procedure successfully completed.
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T2';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ------------------- --- ---------- ------------
SYS_STUWSDP8IKNLLR9QA4XVKCO0BY VARCHAR2 YES UPPER("A") 1
A VARCHAR2 NO 1
SQL>
SQL> set autotrace trace exp
SQL> select * from t2 where upper(a)='A';
Execution Plan
----------------------------------------------------------
Plan hash value: 1513984157
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1000 | 4000 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T2 | 1000 | 4000 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("T2"."SYS_STUWSDP8IKNLLR9QA4XVKCO0BY"='A')
解決問題了
如果頻繁使用表示式,也可以考慮在定義table時 定義虛擬列 (頻繁使用的前提)
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> show user
USER is "XH"
SQL> create table t2 (a int ,a_to_char as (to_char(a)));
create table t2 (a int ,a_to_char as (to_char(a)))
*
ERROR at line 1:
ORA-00902: invalid datatype
11g才支援
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE 11.1.0.6.0 Production
TNS for Linux: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production
SQL> show user
USER is "XH"
SQL> create table t3 (a int ,a_to_char as (to_char(a)));
Table created.
建立 表時候定義虛擬列
SQL> col data_type for a10
SQL> col data_default for a10
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T3';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ---------- --- ---------- ------------
A_TO_CHAR VARCHAR2 NO TO_CHAR("A
")
A NUMBER NO
\
SQL> execute dbms_stats.gather_table_stats('XH','T3');
PL/SQL procedure successfully completed.
SQL> select column_name,data_type,hidden_column,data_default,NUM_DISTINCT from user_tab_cols where table_name='T3';
COLUMN_NAME DATA_TYPE HID DATA_DEFAU NUM_DISTINCT
------------------------------ ---------- --- ---------- ------------
A_TO_CHAR VARCHAR2 NO TO_CHAR("A 1
")
A NUMBER NO 1
SQL> set autotrace trace exp
SQL> select a from t3 where a_to_char='1';
Execution Plan
----------------------------------------------------------
Plan hash value: 4161002650
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 5 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T3 | 1 | 5 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("A_TO_CHAR"='1')
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/12020513/viewspace-624110/，如需轉載，請註明出處，否則將追究法律責任。
相關文章
- C++ 一元謂詞對應的lambda表示式C++
- 表增刪改欄位，及基表改變等相關操作對檢視、同義詞、儲存過程的影響儲存過程
- 謂詞條件的資料型別隨意書寫對SQL效能影響巨大資料型別SQL
- 新特性：/dev/shm對Oracle 11g的影響devOracle
- 從數字鴻溝到數字貧困：負面影響及改進策略
- Oracle 11g 測試停庫對job的影響Oracle
- oracle 11g active dataguard switch over 對ogg的影響Oracle
- oracle 11g對於表壓縮改進Oracle
- ASP中函式呼叫對引數的影響 (轉)函式
- 11g MEMORY_TARGET 引數對SGA 和PGA的影響
- 11g MEMORY_TARGET 引數對SGA 和PGA的影響
- 11g Oracle ORAPWD的改進Oracle
- SQL 改寫系列七：謂詞移動SQL
- SQL 改寫系列六：謂詞推導SQL
- 11g Oracle DBNEWID的改進Oracle
- 【Oracle】-【COMMIT對索引的影響】-從trace看COMMIT對索引的影響OracleMIT索引
- 人工智慧知識的表示——一節謂詞邏輯&產生式&框架人工智慧框架
- 技術基礎 | 在Apache Cassandra中改變VNodes數量的影響Apache
- oracle passwordfile作用 &11g改進Oracle
- 【轉lis的文章】11g MEMORY_TARGET 引數對SGA 和PGA的影響
- 嚴格模式對parseInt()函式的影響模式函式
- JVM 引數調整對 sortx 的影響JVM
- 修改系統時間對oracle的影響Oracle
- Oracle主鍵選擇對插入的影響Oracle
- oracle 索引升降序及排序條件 對查詢計劃的影響Oracle索引排序
- Iowait的成因、對系統影響及對策--systemtapAI
- 索引及排序對執行計劃的影響索引排序
- 數串排序 關鍵詞 sorted lambda表示式排序
- 各平臺影響oracle Process數的引數(轉)Oracle
- 嚴格模式下對變數宣告的影響模式變數
- 修改主機時區對Oracle的影響分析Oracle
- oracle點陣圖索引對DML操作的影響Oracle索引
- 磁碟排序對Oracle資料庫效能的影響排序Oracle資料庫
- Cirium：資料揭示新冠肺炎對中國航空業的影響及對全球航空旅遊增長的影響
- C++謂詞C++
- GPFS Persistent Reserve 的設定對Oracle RAC 的影響Oracle
- 【CURSOR】Oracle繫結變數、執行計劃對遊標的影響Oracle變數
- 網站名稱改動對SEO有什麼影響？網站