C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.InteropServices;

namespace YourNamespace
{
    internal static class NativeMethods
    {
        [DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
        internal static extern int StrCmpLogicalW(string aString, string bString);
    }

    internal class SortableList<T> : BindingList<T>
    {
        protected override bool SupportsSortingCore
        {
            get
            {
                return true;
            }
        }

        protected override void ApplySortCore(PropertyDescriptor prop, ListSortDirection direction)
        {
            int modifier = direction == ListSortDirection.Ascending ? 1 : -1;
            if (prop?.PropertyType.GetInterface("IComparable") != null)
            {
                var items = Items.ToList() as List<T>;
                items.Sort(new Comparison<T>((a, b) =>
                {
                    var aVal = prop.GetValue(a).ToString() as string;
                    var bVal = prop.GetValue(b).ToString() as string;
                    return NativeMethods.StrCmpLogicalW(aVal, bVal) * modifier;
                }));
                Items.Clear();
                foreach (var i in items) Items.Add(i);
            }
        }
    }
}

Quote:

C#

cnn = new MySqlConnection(connectionString);
cnn.Open();
...
cmd.Connection = cnn;
cnn.Open();
cmd.ExecuteNonQuery();

Quote:

SQL

select * from login where userid=@userid, password=@password, confirmpassword=@confirmpassword where loginid=@loginid is same

Quote:

C#

cmd.Parameters.AddWithValue("@userid", id);
//cmd.Parameters.AddWithValue("@employee_id", Convert.ToInt32(id));
cmd.Parameters.AddWithValue("@password", password);
//cmd.Parameters.AddWithValue("@confirmpassword", confirmpassword);

string connectionString;
                MySqlConnection cnn;
                connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
                cnn = new MySqlConnection(connectionString);
                //cnn.Open();
                string id = textBox9.Text;
                string password = textBox10.Text;
                string loginid = "";
                textBox9.Text = "";
                textBox10.Text = "";
                string query = "select * from login where userid=@userid and password=@password and loginid=@loginid";
                using (MySqlCommand cmd = new MySqlCommand(query))
                {
                    cmd.Parameters.AddWithValue("@userid", id);
                    //cmd.Parameters.AddWithValue("@employee_id", Convert.ToInt32(id));
                    cmd.Parameters.AddWithValue("@password", password);
                    cmd.Parameters.AddWithValue("@loginid", loginid);
                    //cmd.Parameters.AddWithValue("@confirmpassword", confirmpassword);
                    cmd.Connection = cnn;
                    cnn.Open();
                    cmd.ExecuteNonQuery();
                    DialogResult dr = MessageBox.Show("Are you sure to Login now?", "Confirmation", MessageBoxButtons.YesNo);
                    if (dr == DialogResult.Yes)
                    {
                        MessageBox.Show("Login Successfully");
                        cnn.Close();
                        this.Hide();
                        Form2 f2 = new Form2();
                        f2.ShowDialog();
                    }
                    else if (dr == DialogResult.No)
                    {
                        MessageBox.Show("Please Enter Correct Login details");
                    }
                }
            }
            else
            {
                MessageBox.Show("Please Enter details to Login");
            }
        }

cnn.Open();
int result = cmd.ExecuteNonQuery(); // always capture the result
cnn.Close();
if (result == 1)
{
    MessageBox.Show("Login was successful");
}
else
{
    MessageBox.Show("The entered details were not correct");
}

if (textBox9.Text != "" && textBox10.Text != "")
            {
                string connectionString;
                MySqlConnection cnn;
                connectionString = @"Data Source=localhost;Initial Catalog=testDB;User ID=root;Password=mysql";
                cnn = new MySqlConnection(connectionString);
                string id = textBox9.Text;
                string password = textBox10.Text;
                textBox9.Text = "";
                textBox10.Text = "";
                string query = "select * from login where userid=@userid and password=@password";
                using (MySqlCommand cmd = new MySqlCommand(query))
                {
                   cmd.Parameters.AddWithValue("@userid", id);
                   cmd.Parameters.AddWithValue("@password", password);
                    cmd.Connection = cnn;
                    cnn.Open();
                    cmd.ExecuteNonQuery();
                    DialogResult dr = MessageBox.Show("Are you sure to Login now?", "Confirmation Message", MessageBoxButtons.YesNo);
                    if (dr == DialogResult.Yes)
                    {
                        MessageBox.Show("Login Successfully");
                        cnn.Close();
                        this.Hide();
                        Form2 f2 = new Form2();
                        f2.ShowDialog();
                    }
                    else if (dr == DialogResult.No)
                    {
                        MessageBox.Show("Please Enter Correct Login details");
                    }
                }
            }
            else
            {
                MessageBox.Show("Please Enter With Correct Login Details");
            }