During SQL Server interviews, it is common for interviewers to ask questions that may not be used in daily life but are important to understand. One such question is about the Left Semi Join Showplan Operator.

When examining the execution plan in text format, there are several interesting types of join operations that can be observed:

Left Semi Join Showplan Operator

The Left Semi Join operator returns each row from the first (top) input when there is a matching row in the second (bottom) input. If no join predicate exists in the Argument column, each row is considered a matching row.

Left Anti Semi Join Showplan Operator

The Left Anti Semi Join operator returns each row from the first (top) input when there is no matching row in the second (bottom) input. If no join predicate exists in the Argument column, each row is considered a matching row.

Right Anti Semi Join Showplan Operator

The Right Anti Semi Join operator outputs each row from the second (bottom) input when a matching row in the first (top) input does not exist. A matching row is defined as a row that satisfies the predicate in the Argument column. If no predicate exists, each row is considered a matching row.

Right Semi Join Showplan Operator

The Right Semi Join operator returns each row from the second (bottom) input when there is a matching row in the first (top) input. If no join predicate exists in the Argument column, each row is considered a matching row.

Let’s take a look at an example script that demonstrates the Left Anti Semi Join Showplan Operator:

USE AdventureWorks;
GO

SET SHOWPLAN_TEXT ON;
GO

SELECT ProductID 
FROM Production.Product 
WHERE ProductID NOT IN (SELECT ProductID FROM Production.WorkOrder);
GO

SET SHOWPLAN_TEXT OFF;
GO

In this example, we are selecting the ProductID from the Production.Product table where the ProductID is not present in the ProductID column of the Production.WorkOrder table. By enabling the SHOWPLAN_TEXT option, we can view the execution plan and observe the Left Anti Semi Join Showplan Operator in action.

Understanding these join showplan operators can be beneficial when analyzing and optimizing query performance. By knowing how different join types are executed, you can make informed decisions when designing and troubleshooting SQL Server queries.