SQL Server Nested Loop Join Operator – Part2

Hi Geeks,

If you missed my yesterday’s post SQL Server nested loop join part1, you can read that by clicking here before today’s post.

Let us change our query from yesterday and add a filter on TerritoryID.

USE [AdventureWorks2012]

SELECT EMP.BusinessEntityID
FROM HumanResources.Employee EMP
	INNER JOIN Sales.SalesPerson AS SLS
	ON EMP.BusinessEntityID = SLS.BusinessEntityID
	WHERE SLS.TerritoryID = 6

NLJoinGrphPlan

Outer input is again SalesPerson but this time it is not using index scan. The new predicate is using TerritoryID and this column is not part of any index and as such query optimizer decides to perform an index scan. Only 2 records qualify filtering criteria and for the same reason clustered index which is the inner input is executed 2 times.

IndxSeekToolTip

In case of nested loop joins, cost of the algorithm is proportional to the size of the outer input multiplied by the size of the inner input. More likely, this operator is picked by query optimizer when outer input is small and inner input has an index on join key.

That’s it for today, see you tomorrow with a new operator, till then.

Happy learning!

Regards,

Kanchan

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About Kanchan Bhattacharyya

Kanchan is an astute IT professional, a seasoned SQL Database Administrator with 13+ years of industry experience. A calculated risk taker with deep technical knowledge and has gained proficiency in database consulting and solutions across different environments. Kanchan holds MBA degree in IT and an International Executive MBA in Project Management. He is very passionate about SQL Server and holds MCSE (Data Platform), MCSA – SQL 2012, MCITP – SQL 2008 certifications. Currently he is focusing on cloud and latest releases of SQL Server. When not working, Kanchan likes to spend his time reading on new technical developments specifically on SQL Server and other related technologies.

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