我加入了"loop join"提示来强迫优化器使用nested loopsjoin.和"set statistics profile on" 一起运行得到如下的执行计划: Rows Executes 3 1 |--Nested Loops(Inner Join, WHERE:([C].[Cust_Id]=[S].[Cust_Id])) 3 1 |--Table Scan(OBJECT:([Customers] AS [C])) 12 3 |--Table Scan(OBJECT:(...
Update 7/18/2011:The cost that I describe above refers to a naive nested loops join in which we have no indexes and in which every outer row is compared to every inner row. Below, I describe how SQL Server can use an index on the inner table to reduce this cost so that it is pro...
1.嵌套循环连接(Nested Loops)适用范围 两个表, 一个叫外部表, 一个叫内部表. 如果外部输入非常小,而内部输入非常大并且已预先建立索引,那么嵌套循环联接将特别有效率。 关于连接时哪个表为outer表,哪个为inner表,我发现sql server会自动给你安排,和你写的位置无关,它自动选择数据量小的表为outer表, 数据量大...
Update 7/18/2011:The cost that I describe above refers to a naive nested loops join in which we have no indexes and in which every outer row is compared to every inner row. Below, I describe how SQL Server can use an index on the inner table to reduce this cost so that it is pro...
Nested Loops Join(嵌套连接) Sql Server支持三种物理连接:nested loops join,merge join和hash join.这篇文章,我将描述nested loops join (或者简称为NL)。 基本算法 最简单的情况是,nested loop会以连接谓词为条件取出一张表里的每一行(称为外部表)
In my past two posts, I explained how SQL Server may add a sort to the outer side of a nested loops join and showed how this sort can significantly improve performance. In an earlier post, I discussed how SQL Server can use random prefetching to improve the performance of a nested loops...
The nested loops join, also called nested iteration, uses one join input as the outer input table (shown as the top input in the graphical execution plan) and one as the inner (bottom) input table. The outer loop consumes the outer input table row by row. The inner loop, executed for...
2011-11-21 16:13 −1.嵌套循环连接(Nested Loops)适用范围两个表, 一个叫外部表, 一个叫内部表. 如果外部输入非常小,而内部输入非常大并且已预先建立索引,那么嵌套循环联接将特别有效率。 关于连接时哪个表为outer表,哪个为inner表,我发现sql server会自动给你安排,和你写的位置无关,它自动... ...
The Nested Loops operator performs the inner join, left outer join, left semi join, and left anti semi join logical operations. Nested loops joins perform a search on the inner table for each row of the outer table, typically using an index. Microsoft SQL Server decides, based on anticipated...
Sql Server支持三种物理连接:nested loops join,merge join和hash join.这篇文章,我将描述nested loops join (或者简称为NL)。 基本算法 最简单的情况是,nested loop会以连接谓词为条件取出一张表里的每一行(称为外部表) 与另外一张表(称为内部表)的每一行进行比较来寻找符合条件的行。(注意这里的"内部"和"外...