static string constring = System.Configuration.ConfigurationManager.ConnectionStrings["Restaurant"].ConnectionString;
        SqlConnection konekcija = new SqlConnection(constring);
        public LogIn()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string username = textBox1.Text;
            string password = textBox2.Text;
            string stringServer = "SELECT S.Server_password as pass FROM Server as S WHERE S.Server_username LIKE '"+ username +"'";
            string stringManager = "SELECT M.Manager_password as pass FROM Manager as M WHERE M.Manager_username LIKE '" + username + "'";
            string stringKitchen = "SELECT K.Kitchen_staff_password as pass FROM Kitchen_staff as K WHERE K.Kitchen_staff_username LIKE '" + username + "'";
            string stringHostess = "SELECT H.Hostess_password as pass FROM Hostess as H WHERE H.Hostess_username LIKE '" + username + "'";

            SqlCommand komandaManager = new SqlCommand(stringHostess, konekcija);
            string komanda = "" + stringServer + "; " + stringManager + "; " + stringKitchen + "; " + stringHostess;
            SqlDataAdapter adapter = new SqlDataAdapter(komanda, konekcija);
            adapter.TableMappings.Add("Table", "Server");
            adapter.TableMappings.Add("Table1", "Manager");
            adapter.TableMappings.Add("Table2", "Kitchen");
            adapter.TableMappings.Add("Table3", "Hostess");

            DataSet ds = new DataSet();

            try
            {
                konekcija.Open();
                adapter.Fill(ds);
                if (ds.Tables["Server"].Rows.Count != 0)
                {
                    string s = Convert.ToString(ds.Tables["Server"].Rows[0]["pass"]);
                    if (password.Equals(s))
                    {
                        this.Hide();
                        Hello_Server f = new Hello_Server();
                        f.ShowDialog();
                    }
                    else
                    {
                        MessageBox.Show("Невалиднa лозинка!");
                    }
                }
                else if (ds.Tables["Manager"].Rows.Count != 0)
                {
                    string s = Convert.ToString(ds.Tables["Manager"].Rows[0]["pass"]);
                    if (password.Equals(s))
                    {
                        this.Hide();
                        Hello_Server f = new Hello_Server();
                        f.ShowDialog();
                    }
                    else
                    {
                        MessageBox.Show("Невалиднa лозинка!");
                    }
                }
                else if (ds.Tables["Kitchen"].Rows.Count != 0)
                {
                    string s = Convert.ToString(ds.Tables["Kitchen"].Rows[0]["pass"]);
                    if (password.Equals(s))
                    {
                        this.Hide();
                        Hello_Hostess f = new Hello_Hostess();
                        f.ShowDialog();
                    }
                    else
                    {
                        MessageBox.Show("Невалиднa лозинка!");
                    }
                }
                else if (ds.Tables["Hostess"].Rows.Count != 0)
                {
                    string s = Convert.ToString(ds.Tables["Hostess"].Rows[0]["pass"]);
                    if (password.Equals(s))
                    {
                        this.Hide();
                        Hello_Server f = new Hello_Server();
                        f.ShowDialog();
                    }
                    else
                    {
                        MessageBox.Show("Невалиднa лозинка!");
                    }
                }
                else if (ds.Tables[0].Rows.Count == 0 || ds.Tables[1].Rows.Count == 0 ||
                    ds.Tables[2].Rows.Count == 0 || ds.Tables[3].Rows.Count == 0)
                {
                    MessageBox.Show("Невалидни корисничко име и лозинка!");
                }
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message);
            }
            finally
            {
                konekcija.Close();
            }
        }