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Thursday, January 30, 2014
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How to Querying Data using Joins in Sql Programming: Part 2

8:57 AMThursday, January 30, 2014
In comparison to an inner join, an outer join displays the result set containing all the rows from one table and the matching rows from another table. For example, if you create an outer join on Table A and Table B, it will show you all the records of Table A and only those records from Table B for which the condition on the common column holds true.

An outer join displays NULL for the columns of the related table where it does not find matching records. The syntax of applying an outer join is:

SELECT column_name, column_name [, column_name]
FROM table1_name [LEFT | RIGHT| FULL] OUTER JOIN table2_name
ON table_name.ref_column_name

An outer join is of three types:

Left Outer Join

A left outer join returns all rows from the table specified on the left side of the LEFT OUTER JOIN keyword and the matching rows from the table specified on the right side. The rows in the table specified on the left side for which matching rows are not found in the table specified on the right side, NULL values are displayed in the column that get data from the table specified on the right side.

Consider an example. The SpecialOfferProduct table contains a list of products that are on special offer. The SalesOrderDetail table stores the details of all the sales transactions. The users at AdventureWorks need to view the transaction details of these products. In addition, they want to view the ProductID of the special offer products for which no transaction has been done.

To perform this task, you can use the LEFT OUTER JOIN keyword, as shown in the following query:

Select p.ProductID, q.SalesOrderID, q.UnitPrice
From Sales.SpecialOfferProduct p
Left outer join Sales.SalesOrderDetail q on p.ProductID= q.ProductID
where SalesOrderID is NULL

The following figure displays the output of the preceding query.

How to Querying Data using Joins in Sql Programming: Part 2

Right Outer Join

A right outer join returns all the rows form the table specified on the right side of the RIGHT OUTER JOIN keyword and the matching rows from the table specified on the left side.

Consider the example of Adventure Works. Inc. The JobCandidate table stores the details of all the job candidates. You need to retrieve a list of all the job candidates. In addition, you need to find which candidate has been employed in Adventure Works, Inc. To perform this task, you can apply a right outer join between the Employee and JobCandidate tables, as shown in the following query:

SELECT e.JobTitle, d.JobCandidateID
FROM HumanResources.Employee e
RIGHT OUTER JOIN HumanResources.JobCandidate d
ON e.BusinessEntityID=d.BusinessEntityID

The result set displays the JobCandidateID column from the JobCandidate table and the BusinessEntityID column from the matching rows of the Employee table.

How to Querying Data using Joins in Sql Programming: Part 2

Full Outer Join

A full outer join is a combination of left outer join and right outer join. This join returns all the matching and non-matching rows from both the tables. However, the matching records are displayed only once. In case of non-matching rows, a NULL value is displayed for the columns for which data is not available.

SELECT e.BusinessEntityID, e.EmployeeName,ed.EmployeeEducationCode,
ed. Education
FROM Employee e FULL OUTER JOIN Education ed
ON e.EmployeeEducationCode = ed.EmployeeEducationCode

According to this query, the employee details and their highest educational qualification is displayed. For non-matching values, NULL is displayed.

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