Project/project/Vhod.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace project
{
    public partial class Vhod : Form
    { 
        public Vhod()
        {
            InitializeComponent();
        }

        private void Vhod_FormClosed(object sender, FormClosedEventArgs e)
        {
            Application.Exit();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (polelogin.Text.Replace(" ", "") == "") MessageBox.Show("Поле логин не может быть пустым");
            else if (polepassword.Text.Replace(" ", "") == "") MessageBox.Show("Поле пароль не может быть пустым");
            else
            {
                SqlConnection sqlconn = new SqlConnection(@"Data Source=ngknn.ru;Initial Catalog=Project_GorodskoiSpravochnik;Persist Security Info=True;User ID=31П;Password=12357");
                string query = "Select *from Employee where login = '" + polelogin.Text.Trim() + "' and password = '" + polepassword.Text.Trim() + "'";
                SqlDataAdapter sda = new SqlDataAdapter(query, sqlconn);
                DataTable dtbl = new DataTable();
                sda.Fill(dtbl);
                if (dtbl.Rows.Count == 1)
                {
                    Login.login = polelogin.Text.Trim();
                    this.Hide();
                    Main Main = new Main();
                    Main.ShowDialog();
                }
                else
                {
                    MessageBox.Show("Неверный логин и/или пароль");
                }
            }
        }

    }
}