英文: 1 Base cardinality is the number of rows in a base table. 中文: 基本的行集数是一个表的行数。 更详细... 英文: 3 Join cardinality is the number of rows produced when two row sets are joined together. 中文: 连接行集数是两个行集被连接在一起时产生的行集数。 更详细... 英...
如下截图所示: Actual Number of Rows 与 Esimated Number of Rows 优化器有很多方式估算基数的算法,我们这里列举几种简单的方式,如果你想了解更多基数估计的算法。可以参考”SQL Server中关于基数估计如何计算预估行数的一些探讨“或官方文档Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator...
没有建立一个没有……的 笛卡尔产品的R和S的基数……cardinality 基数 金软件山 英汉双解计算机词典 cardinality "In a relation data base, the number of tuples in a relation.关系数据库中,一个关系的元组数目。
如下所示,Esimated Number of Rows的取值就来源于AVG_RANGE_ROWS . 因为11222位于11185 与 11223之间。所以取RANGE_HI_KEY=11223这条记录对应的AVG_RANGE_ROWS(4.32432)。 3: 如果在查询条件中使用变量(编译时未知特定搜索值),则预估行数(Esimated Number of Rows)= 密度* 采样的行数: [Row Sampled ]* [A...
美 英[kɑːdɪ'nælɪtɪ] n.〔数〕基数 网络基数性;势;基数或势 英汉 网络释义 n. 1. 〔数〕基数 释义: 全部,〔数〕基数,基数性,势,基数或势
Generate the access plan and see what the optimizer estimates the total cardinality (Number of rows) returned by the query will be. 生成访问计划,查看优化器对该查询返回的总基数(行数)的估计值。 www.ibm.com 7. When examining an access plan, you may find that the estimated cardinality is not...
Description: We observed that spatial index cardinality estimate is based on the total number of rows of the table. While the documentation does not state such behavior : https://dev.mysql.com/doc/mysql-infoschema-excerpt/8.0/en/information-schema-statistics-ta... https://dev.mysql.com/doc/...
Cardinality: In set theory, it is the number of elements in a set. In databases, it will be the number of rows in a table or after applying a predicate. Selectivity: Fraction of records returned after applying a predicate. For example, a table containing people and about one third of th...
If the cardinality for flight_id in Flights is 250, then the selectivity of the predicate is 1/250. The optimizer would estimate the number of rows read to be: ((Rows in Flights) * (Rows in OtherTable))/250Parent topic: Selectivity and cardinality statistics Related...
Relationships exist between two query subjects or between tables within a query subject. The cardinality of a relationship is the number of related rows for each of the two objects in the relationship. The rows are related by the expression of the relati