LOGIN FORM USING C# & Sql Server

Login Credential from sqlserver database

 using System;   
 using System.Collections.Generic;   
 using System.ComponentModel;   
 using System.Data;   
 using System.Drawing;   
 using System.Linq;   
 using System.Text;   
 using System.Windows.Forms;   
 using System.Data.Sql;   
 using System.Data.OleDb;   
 using System.Data.SqlClient;   
 namespace login_form   
 {   
   public partial class Form1 : Form   
   {   
     SqlConnection con = new SqlConnection();   
     public Form1()   
     {   
       SqlConnection con = new SqlConnection();   
       con.ConnectionString = "Data Source=KRISHNA-PC\\SQLEXPRESS;Initial Catalog=STUDENT;Integrated Security=True";   
       InitializeComponent();   
     }   
     private void Form1_Load(object sender, EventArgs e)   
     {   
       
       SqlConnection con = new SqlConnection("Data Source=Home-PC\\SQLEXPRESS;Initial Catalog=STUDENT;Integrated Security=True");   
       con.Open();   
       {   
       }   
     }   
     private void button1_Click(object sender, EventArgs e)   
     {   
       SqlConnection con = new SqlConnection();   
       con.ConnectionString = "Data Source=Home-PC\\SQLEXPRESS;Initial Catalog=STUDENT;Integrated Security=True";   
       con.Open();   
       string userid = textBox1.Text;   
       string password = textBox2.Text;   
       SqlCommand cmd = new SqlCommand("select userid,password from login where userid='" + textBox1.Text + "'and password='" + text      Box2.Text + "'", con);   
       SqlDataAdapter da = new SqlDataAdapter(cmd);   
       DataTable dt = new DataTable();   
       da.Fill(dt);   
       if (dt.Rows.Count > 0)   
       {   
         MessageBox.Show("Login sucess Welcome to Homepage https://logicerrors.blogspot.in/");   
         System.Diagnostics.Process.Start("https://logicerrors.blogspot.in/");   
       }   
       else   
       {   
         MessageBox.Show("Invalid Login please check username and password");   
       }   
       con.Close();   
     }   
     private void button2_Click(object sender, EventArgs e)   
     {   
       Application.Exit();   
     }   
   }   
 }