Как заполнить textBox из базы sql?

            NpgsqlConnection conn = new NpgsqlConnection(Conection_string);
            conn.Open();
 
            string SQL_foto = "SELECT COUNT (DISTINCT \"Money\".date) FROM \"Money\" where \"Money\".login_user='" + login_user + "' and \"Money\".type_operation ='" + type_operacii + "';";
           
            NpgsqlCommand command = new NpgsqlCommand(SQL_foto,conn);
            object price = command.ExecuteScalar();
            conn.Close();
textBox1.Text=price.toString();

string SQL_foto = "SELECT COUNT (DISTINCT \"Money\".date) FROM \"Money\" where \"Money\".login_user='" +
    login_user + "' and \"Money\".type_operation ='" + type_operacii + "';";

 private void comboBox1_DropDownClosed(object sender, EventArgs e)
{
NpgsqlConnection conn = new NpgsqlConnection(Conection_string);
            conn.Open();
 
            string SQL_foto = "SELECT "Телефон" FROM "Люди" where "Люди".ФИО='" + comboBox1.Text + "' ";
           
            NpgsqlCommand command = new NpgsqlCommand(SQL_foto,conn);
            object telefon = command.ExecuteScalar();
            conn.Close();
textBox1.Text = telefon.toString();
}

        string Connection_string;
        private void comboBox1_DropDownClosed(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection(Connection_string);
            conn.Open();
 
            string SQL_foto = string SQL_foto = "SELECT "Телефон" FROM "Люди" where "Люди".ФИО='" + comboBox1.Text + "' ";
            SqlCommand command = new SqlCommand(SQL_foto, conn);
 
            object price = command.ExecuteScalar();
            conn.Close();
        }