Thursday, May 10, 2012

LINQ to SQL – Select with AGGREGATE (GROUP BY)


LINQ to SQL – INNER JOIN

Before writing a LINQ to SQL query, we first need to create a DataContext using the LINQ to SQL Classes template, to know more on how to create the DataContext refer to the post LINQ to SQL Sample

Once the DataContext is created we can query the Object model using LINQ queries, let us consider the Employee table which has the following structure.



In practical situations we will have to join more than one table to get the details for reporting.

An INNER JOIN is used to fetch the matching details from 2 or more tables.

Assume we have the following data in the Employee and Department Tables

Table: Employee




ID
NAME
Phone
Email
DepartmentID
Salery
1
Tom
123-123-1234
tom@abcsoftware.com
1
5000
2
Harry
123-123-1234
harry@abcsoftware.com
2
6000
3
Peter
111-222-3333
peter@abcsoftware.com
3
6500
4
John
111-222-3333
john@abcsoftware.com
3
7500
5
Charles
666-444-2222
charles@abcsoftware.com
NULL
6500

Table: Department
ID
NAME
1
Finance
2
Human Resources
3
IT
4
Sales
5
Marketing

The INNER JOIN SQL Query to join the 2 tables is as follows

SELECT     E.ID, E.Name, E.Phone, D.Name AS Department
FROM         Employee AS E INNER JOIN
                      Department AS D ON E.DepartmentID = D.ID

This query will fetch the following data
ID
NAME
Phone
Department
1
Tom
123-123-1234
Finance
2
Harry
123-123-1234
Human Resources
3
Peter
111-222-3333
IT
4
John
111-222-3333
IT

Now let us see how the same can be achieved using a LINQ query.

EmployeeClassesDataContext dbContext = new EmployeeClassesDataContext();

var emp = (from e in dbContext.Employees
                       join d in dbContext.Departments
                       on e.DepartmentID equals d.ID
                       select new { e.ID, e.Name, e.Phone, Department = (d.Name) });





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