how to check duplicate record before insert in asp.net

In this  article I will explain how to  check duplicate record before insert in asp.net  using Stored Procedure 

Step1 - Create table and Stored Procedure 

GO

/****** Object:  Table [dbo].[tbl_Login]    Script Date: 7/5/2016 10:56:06 AM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[tbl_Login](
[Id] [int] IDENTITY(1,1) NOT NULL,
[UserName] [nvarchar](50) NULL,
[Password] [nvarchar](50) NULL,
 CONSTRAINT [PK_tbl_Login] PRIMARY KEY CLUSTERED 
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO


insert into tbl_Login (Username,Password)values('admin',123456)
select * from tbl_Login


CREATE PROCEDURE Insertintologin
    @Username varchar(100),
    @Password varchar(100)
 
AS
BEGIN
    SET NOCOUNT ON;

    IF EXISTS(SELECT * FROM tbl_Login WHERE Username = @Username)
    BEGIN
        SELECT 'FALSE'
    END
    ELSE
    BEGIN
        INSERT INTO tbl_Login(Username, Password)
        VALUES(@Username, @Password)
        SELECT 'TRUE'
    END
END
GO

Step 2- Add aspx page with two textbox one login button and label

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="txtusername" placeholder="username" runat="server"></asp:TextBox>
        <br />
        <asp:TextBox ID="txtpassword"  placeholder="password" TextMode="Password"  runat="server"></asp:TextBox>
        <br />

        <asp:Button ID="btnlogin" runat="server" Text="Login" OnClick="btnlogin_Click" />
        <br />
        <asp:Label ID="lblmassage" runat="server" Text="" ></asp:Label>
    </div>
    </form>
</body>
</html>

Step3- Add connection String in webconfig

<connectionStrings>
<add name="dbconnection" connectionString="Data Source=DESKTOP-TGH3GB7;Integrated Security=true;Initial Catalog=sample"/>
</connectionStrings>

Step4- Add below code on code behind .

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void btnlogin_Click(object sender, EventArgs e)
    {
        string strConnString = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;
        using (SqlConnection con = new SqlConnection(strConnString))
        {
            using (SqlCommand cmd = new SqlCommand("Insertintologin"))
            {
                cmd.Connection = con;
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@Username", txtusername.Text.Trim());
                cmd.Parameters.AddWithValue("@Password", txtpassword.Text.Trim());
               
                con.Open();
                bool check = Convert.ToBoolean(cmd.ExecuteScalar());
                if (check)
                {
                    txtusername.Text = string.Empty;
                    txtpassword.Text = string.Empty;

                    lblmassage.Text = "Data inserted Successfully!";
                   
                }
                else
                {
                    txtusername.Text = string.Empty;
                    txtpassword.Text = string.Empty;
                    lblmassage.Text = "Username exists!";
                    
                }
                con.Close();
            }
        }
    }
}

Snapshot 








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