Calculated as 1 / distinct values for all values in the first key column of the statistics object, excluding the histogram boundary values. This Density value is not used by the query optimizer and is displayed for backward compatibility with versions before SQL Server 2008. 但是这里发现头部信息(...
from table_name where column_name not in (histogram range_hi_key values)) 具体到这个例子来说(对于复合索引,这个字段是符合索引第一个字段),如下所示: SELECTCOUNT(DISTINCTCustomerID)*1.0/COUNT(*) FROMSales.SalesOrderHeader WHERECustomerIDNOTIN( 11000, 11019, 11091, 11142, 11185, 11223, 11262, 1...
如果你说的是set的cardinality，那么cardinality就是集合中元素的个数。那么，你可能会问：直接叫count不...
CREATEDATABASEIFNOTEXISTS`test`;USE`test`;SETNAMESutf8mb4;SETFOREIGN_KEY_CHECKS=0;DROPTABLEIFEXISTS`order`;CREATETABLE`order`(`id`bigintNOTNULLDEFAULT''AUTO_INCREMENTCOMMENT'主键',`uid`bigintNOTNULLDEFAULT''COMMENT'用户id',`desc`varchar(255)CHARACTERSETutf8COLLATEutf8_general_ciNOTNULLDEFAULT''...
SQL> create table t as select * from dba_objects where 1=0;Table created.SQL> create index ...
The terms "highcardinality" and "lowcardinality" are frequently used when discussing table columns. A highcardinalitycolumn means that a column has many unique values. For example, a primary key c Oracle 数据库 原创 maclean_007 2011-08-08 16:15:43 ...
简介:CBO中基数(cardinality)、可选择率(selectivity)的计算公式 Cardinality(基数)是Oracle预估的返回行数,即对目标SQL的某个具体执行步骤的执行结果所包含记录数的估算值。 CBO中基数(cardinality)、可选择率(selectivity)的计算公式 Cardinality(基数)是Oracle预估的返回行数,即对目标SQL的某个具体执行步骤的执行结果所...
5 rows in set (0.00 sec) 通过explian查看时,发现sql用的是主键PRIMARY,而不是obj_type索引。通过show index 查看索引的Cardinality值,发现这个值是实际数据的两倍。感觉这个Cardinality值已经不正常,因此通过analyzea table命令对这个值从新进行了计算。命令执行完毕后,就可用使用索引了。
Subclause 6.28, "<numeric value function>": <max cardinality expression> ::= ARRAY_MAX_CARDINALITY <left paren> <array value expression> <right paren> ... Conformance Rules: Without Feature S403, "ARRAY_MAX_CARDINALITY", conforming SQL language shall not contain <max cardinality expres...
This Oracle tutorial explains how to use the Oracle / PLSQL CARDINALITY function with syntax and examples. The Oracle / PLSQL CARDINALITY function returns the number of elements in a nested table.