All posts by Basavaraj Biradar

SQL Server APPLY operator

Sql Server, , , , , , ,

APPLY operator was introduced in Sql Server 2005. The main purpose of the APPLY operator is to JOIN a Table with a Table Valued User Defined Function. The APPLY operator invokes/executes the Table Valued User Defined Function for each row returned by the LEFT side table expression of the APPLY operator.

APPLY operator can be used to join two table expressions just like any other JOIN operators. In case of APPLY operator, for each row in the LEFT side table expression of the APPLY operator the RIGHT side table expression is evaluated and final result can have the columns from both LEFT and RIGHT side table expressions just like in any other JOIN operations result.

Unlike APPLY operator, classic joins like INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN etc, doesn’t support evaluating a RIGHT side table valued function based on the column values of each row returned by the LEFT side table expression.

In other words the classic joins works on the self-sufficient sets of data, where these sets of data doesn’t depend on one another. Where-as in case of APPLY OPERATOR the RIGHT side data set is not self-sufficient, instead the APPLY operator uses values from the LEFT side table expression to define the RIGHT side data set.

Types of APPLY operators in Sql Server

There are two types of APPLY operators in Sql Server

CROSS APPLY

This operator returns only those rows from the LEFT side table expression of the CROSS APPLY operator which produces the result from the RIGHT side Table expression. So from the result perspective we can say that the CROSS APPLY is similar to that of the classic INNER JOIN operation

To understand CROSS APPLY with extensive list of examples, you may like to read CROSS APPLY in Sql Server

OUTER APPLY

This operator returns all the rows from the LEFT side table expression of the OUTER APPLY operator irrespective of whether it produces the corresponding result in the RIGHT side table expression or not. The RIGHT side table expression columns value will be NULL in the final result for those rows in the LEFT table expression that don’t produce the result from the RIGHT side table expression. So from the result perspective we can say that the OUTER APPLY is similar to the classic LEFT OUTER JOIN

To understand OUTER APPLY with extensive list of examples, you may like to read OUTER APPLY in Sql Server

Difference between LEFT OUTER JOIN and RIGHT OUTER JOIN in Sql Server

Differences, Sql Server, , , , , ,

This article provides a comparative analysis of the Sql Server LEFT OUTER JOIN and RIGHT OUTER JOIN with extensive list of examples.

To understand the differences between Sql Server LEFT OUTER JOIN and RIGHT OUTER JOIN, let us create a demo database with two tables Customers and Orders with sample data as shown in the following image by executing the following script:

joins-demo-tables

CREATE DATABASE SqlHintsJoinDemo
GO
USE SqlHintsJoinDemo
GO
--Create Customers Table and Insert records
CREATE TABLE Customers 
( CustomerId INT, Name VARCHAR(50) )
GO
INSERT INTO Customers
VALUES(1,'Shree'), (2,'Kalpana'), (3,'Basavaraj')
GO
--Create Orders Table and Insert records into it
CREATE TABLE Orders (OrderId INT, CustomerId INT)
GO
INSERT INTO Orders 
VALUES(100,1), (200,4), (300,3)
GO

[ALSO READ] Joins In Sql Server

LEFT OUTER JOIN

RIGHT OUTER JOIN
DEFINITION

LEFT OUTER JOIN / LEFT JOIN returns all the rows from the LEFT table and the corresponding matching rows from the right table. If right table doesn’t have the matching record then for such records right table column will have NULL value in the result.

RIGHT OUTER JOIN / RIGHT JOIN returns all the rows from the RIGHT table and the corresponding matching rows from the left table. If left table doesn’t have the matching record then for such records left table column will have NULL value in the result.
VENN DIAGRAM
left-outer-join-venn-diagram

As per the above LEFT OUTER JOIN Venn Diagram, all the records from the left table (Customers) are returned regardless if any of those records have a match in the right table (Orders). It will also return any matching records from the right table (Orders)

 right-outer-join-venn-diagram

As per the above RIGHT OUTER JOIN Venn Diagram, all the rows in the right table (Orders) are returned regardless if any of those records have a match in the left table (Customers). It will also return any matching records from the left table (Customers)
EXAMPLE

As per the data in our demo tables, Customers with CustomerId 1 and 3 in Customers table have the orders in the Orders table. Where as the customer with CustomerId 2 doesn’t have any order in the Orders table. So the LEFT JOIN on the CustomerId column between Customers and Orders table will return the Customer and Order details of the Customers with CustomerId 1 and 3 and for CustomerId 2 the Order Table columns will have NULL value in the result. Let us verify this by executing the following LEFT OUTER JOIN query:

SELECT *
FROM Customers C 
  LEFT OUTER JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
left-outer-join-results

As per the data in our demo tables, only for the order with OrderId 200 we don’t have it’s corresponding customer info with CustomerId 4 in the Customers table. And for the other two orders, the corresponding customer info is present in the Customers Table. So for the orders with CustomerId 1 and 3 will have customer details and for the order with CustomerId 4, the Customers table columns will have NULL value in the result. Let us verify this by executing the following RIGHT OUTER JOIN query:

SELECT *
FROM Customers C 
  RIGHT OUTER JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT
right-outer-join-result

EXECUTION PLAN
Let us execute the following query and verify it’s execution plan:

SELECT *
FROM Customers C 
  LEFT OUTER JOIN Orders O
    ON O.CustomerId = C.CustomerId

left-join-execution-plan

From the execution plan we can see that first all records from the LEFT TABLE (i.e. Customers) of the JOIN clause are fetched. Then for each of these LEFT TABLE (i.e. Customers) records, it is trying to fetch the matching data from the RIGHT TABLE (i.e. Orders TABLE) using Nested Loops LEFT OUTER JOIN operation.

 Let us execute the following query and verify it’s execution plan:

SELECT *
FROM Customers C 
  RIGHT OUTER JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
right-join-execution-plan

From the execution plan we can see that first all records from the RIGHT TABLE (i.e. Orders) of the JOIN clause are fetched. Then for each of these LEFT TABLE (i.e. Orders) records, it is trying to fetch the matching data from the RIGHT TABLE (i.e. Customers TABLE) using Nested Loops LEFT OUTER JOIN operation. From the execution plan we can observe that Sql Server indirectly converted this RIGHT OUTER JOIN query to a LEFT OUTER JOIN query like below before execution:

SELECT *
FROM Orders O 
  LEFT OUTER JOIN Customers O
    ON O.CustomerId = C.CustomerId

So, to get the result from LEFT OUTER JOIN which is same as that of RIGHT OUTER JOIN and vice-versa, we just need to switch the order in which the tables appear in the JOIN clause.
ALTERNATIVE DEFINITION
LEFT JOIN = INNER JOIN + Rows from LEFT Table which doesn’t have matching record in the RIGHT table RIGHT JOIN = INNER JOIN + Rows from RIGHT Table which doesn’t have matching record in the LEFT table

CONCLUSION

The main difference between LEFT OUTER JOIN and RIGHT OUTER JOIN is: LEFT OUTER JOIN returns all records from the LEFT table irrespective of whether there are any matching rows in the RIGHT table. Where as RIGHT OUTER JOIN returns all records from the RIGHT table irrespective of whether there are any matching rows in the LEFT table. To get the result from LEFT OUTER JOIN which is same as that of RIGHT OUTER JOIN and vice-versa, we just need to switch the order in which the tables appear in the JOIN clause.

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Difference between LEFT JOIN and LEFT OUTER JOIN in Sql Server

Differences, Sql Server, , , , , , ,

Frankly speaking, in Sql Server there is no difference between LEFT JOIN and LEFT OUTER JOIN. They produce the same result and also the same performance.

Let us prove with examples that there is no difference between LEFT JOIN and LEFT OUTER JOIN. Execute the following script to create a demo database with two tables Customers and Orders with sample data as shown in the following image:

inner-join-demo-tables

CREATE DATABASE SqlHintsJoinDemo
GO
USE SqlHintsJoinDemo
GO
--Create Customers Table and Insert records
CREATE TABLE Customers 
( CustomerId INT, Name VARCHAR(50) )
GO
INSERT INTO Customers
VALUES(1,'Shree'), (2,'Kalpana'), (3,'Basavaraj')
GO
--Create Orders Table and Insert records into it
CREATE TABLE Orders (OrderId INT, CustomerId INT)
GO
INSERT INTO Orders 
VALUES(100,1), (200,4), (300,3)
GO

[ALSO READ] Joins In Sql Server

LEFT JOIN and LEFT OUTER JOIN produces the same result

Below table demonstrates that both LEFT JOIN and LEFT OUTER JOIN produces the same result.

LEFT JOIN

LEFT OUTER JOIN

 
SELECT * 
FROM Customers C 
  LEFT JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
left-join-results 

SELECT * 
FROM Customers C 
  LEFT OUTER JOIN Orders O
    ON O.CustomerId = C.CustomerId

RESULT:
left-outer-join-results

LEFT JOIN and LEFT OUTER JOIN Execution Plan Comparison

From the below execution plans comparison, we can see that both LEFT JOIN and LEFT OUTER JOIN are producing the same plan and performance. Here I have used the Sql Server 2016 “Compare Execution Plans” feature to compare the execution plan produced by LEFT JOIN and LEFT OUTER JOIN. This feature provides an option to highlight the similar operations and we can see that both LEFT JOIN and LEFT OUTER JOIN is producing the similar operations and they are highlighted in the same color.


left-join-and-left-outer-join-execution-plan-comparision

LEFT JOIN and LEFT OUTER JOIN produces the same performance counters

The below performance counters (i.e. execution plan properties) comparison shows that both LEFT JOIN and LEFT OUTER JOIN produces the same performance result


left-join-and-left-outer-join-execution-plan-properties-comparision

CONCLUSION

From the above various examples we can see that there is absolutely NO DIFFERENCE between LEFT JOIN and LEFT OUTER JOIN. Even though both produces the same result and performance, I would prefer using LEFT OUTER JOIN instead of just LEFT JOIN. As it is more readable and leaves no ambiguity. Please share which one you use and reason for the same.

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