Introduction
Today, in this article let's play around with one of the interesting and most useful concepts in LINQ.
Question: What is inner join using LINQ for multiple tables?
In simple terms "It provides flexibility to pull out the matching result sets from 3 or more tables using a LINQ inner join.".
Step 1: Create a "ASP.NET Web Application", as in:
![new-project-window.jpg]()
Step 2: The design of the Employee table looks like this:
![employee-table.jpg]()
![employee-ID-table.jpg]()
Step 3: The design of the Position table looks like this:
![position-table.jpg]()
![position-ID-table.jpg]()
Step 4: The design of the Salary table looks like this:
![salary-table.jpg]()
![salary-id-table.jpg]()
Step 5: The complete code of WebForm1.aspx looks like this:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs"Inherits="LINQInnerJoinApp._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<center>
<div>
<table>
<tr>
<td colspan="2">
<asp:Label ID="Label1" runat="server" Text="INNER JOIN using LINQ for Multiple Tables (3 Tables)"
Font-Bold="true" Font-Size="Large" Font-Names="Verdana" ForeColor="Maroon"></asp:Label>
</td>
</tr>
<tr>
<td colspan="2" align="center">
<asp:Button ID="Button1" runat="server" Text="Select Data" Font-Names="Verdana"Width="213px"
BackColor="Orange" Font-Bold="True" OnClick="Button1_Click" />
</td>
</tr>
<tr>
<td colspan="2" align="center">
<br />
<asp:GridView ID="GridView1" runat="server" BackColor="LightGoldenrodYellow"BorderColor="Tan"
BorderWidth="1px" CellPadding="2" EnableModelValidation="True" ForeColor="Black"
GridLines="None" AutoGenerateColumns="False">
<AlternatingRowStyle BackColor="PaleGoldenrod"></AlternatingRowStyle>
<FooterStyle BackColor="Tan"></FooterStyle>
<HeaderStyle BackColor="Tan" Font-Bold="True"></HeaderStyle>
<PagerStyle HorizontalAlign="Center" BackColor="PaleGoldenrod"ForeColor="DarkSlateBlue">
</PagerStyle>
<SelectedRowStyle BackColor="DarkSlateBlue" ForeColor="GhostWhite"></SelectedRowStyle>
<Columns>
<asp:BoundField DataField="FirstName" HeaderText="First Name" ReadOnly="true" />
<asp:BoundField DataField="LastName" HeaderText="Last Name" />
<asp:BoundField DataField="Position1" HeaderText="Position" />
<asp:BoundField DataField="Salary1" HeaderText="Salary" />
</Columns>
</asp:GridView>
</td>
</tr>
</table>
</div>
</center>
</form>
</body>
</html>
Step 6: The complete code of WebForm1.aspx.cs looks like this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace LINQInnerJoinApp
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Button1_Click(object sender, EventArgs e)
{
var query =from rin objEntities.Employeejoin p in objEntities.Position on r.EmpId equals p.EmpIdjoin qinobjEntities.Salary on p.PosId equals q.PosIdselect new{r.FirstName,r.LastName,p.Position1,q.Salary1};
GridView1.DataSource = query;
GridView1.DataBind();
}
#region
Instance MembersCompanyEntities objEntities =new CompanyEntities();
#endregion
}
}
Step 7: The output of the application looks like this:
![select-data.jpg]()
Step 8: The results retrieved output of the application looks like this:
![select-data-in-linq.jpg]()