Не обновляется значение rating в бд

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using static System.Windows.Forms.VisualStyles.VisualStyleElement;
using System.Reflection;
using System.Globalization;
using MyHealth.Models;
using System.Data.Common;
 
namespace MyHealth.UCs
{
    public partial class UCDoctors : UserControl
    {
        public UCDoctors()
        {
            InitializeComponent();
            cbxNumber.Items.Add(1.0);
            cbxNumber.Items.Add(2.0);
            cbxNumber.Items.Add(3.0);
            cbxNumber.Items.Add(4.0);
            cbxNumber.Items.Add(5.0);
 
        }
 
        private string connectionString = "Data Source = SHARE-23; Initial Catalog = MyHealth; Trusted_Connection = True;";
        private SqlConnection connection = null;
        private SqlDataAdapter dataAdapter = null;
        private DataTable dtDoctors;
        private SqlDataReader dataReader = null;
 
        private void UCDoctors_Load(object sender, EventArgs e)
        {
            RefreshDGV();
        }
 
        void RefreshDGV()
        {
            string selectAllDoctors = "select * from Doctors;";
            try
            {
                using (connection = new SqlConnection(connectionString))
                {
                    connection.Open();
                    dataAdapter = new SqlDataAdapter(selectAllDoctors, connection);
                    dtDoctors = new DataTable();
                    dataAdapter.Fill(dtDoctors);
                    dgvDoctors.DataSource = dtDoctors;
                    SelectSurname();
                }
            }
            catch
            {
                connection.Close();
            }
        }
 
 
        private void SelectSurname()
        {
            string selectAllDoctors = "select surname_d from Doctors;";
            try
            {
                using (connection = new SqlConnection(connectionString))
                {
                    connection.Open();
                    dataAdapter = new SqlDataAdapter(selectAllDoctors, connection);
                    dtDoctors = new DataTable();
                    dataAdapter.Fill(dtDoctors);
                    cbxDoctors.DisplayMember = "surname_d";
                    cbxDoctors.DataSource = dtDoctors;
                }
            }
            catch
            {
                connection.Close();
            }
        }
 
        private void btnRespect_Click(object sender, EventArgs e)
        {
            //var rating = float.Parse(cbxNumber.SelectedItem.ToString());
            //var rating = float.Parse(cbxNumber.SelectedItem.ToString().Replace(".", ","));
            //var rating = float.Parse(cbxNumber.SelectedItem.ToString(), CultureInfo.InvariantCulture);
            //var rating = float.Parse(cbxNumber.SelectedItem.ToString(), System.Globalization.NumberStyles.AllowDecimalPoint);
            //float rating = float.Parse(cbxNumber.Text+".0", CultureInfo.InvariantCulture.NumberFormat);
            //float rating = (float)Convert.ToDouble(cbxNumber.Text);
            //cbxNumber.Text
            giveRespect(float.Parse(cbxNumber.Text.Replace(".", ",")),cbxDoctors.Text);
 
        }
 
 
       
 
        void giveRespect(float rating, string surname)
        {
            string giveRespectRequest = $"UPDATE Doctors SET Doctors.rating=(Doctors.rating+{rating})/2.0 where Doctors.surname_d = '{surname}';";
            try
            {
                using (connection = new SqlConnection(connectionString))
                {
                    SqlCommand giveRespectComm = new SqlCommand(giveRespectRequest, connection); 
                    giveRespectComm.ExecuteNonQuery();
                }
            }
            catch
            {
                connection.Close();
            }
            finally
            {
                RefreshDGV();
            }
        }
 
        private void btnRefreshTable_Click(object sender, EventArgs e)
        {
            dtDoctors.Clear();
            RefreshDGV();
        }
    }
}

void giveRespect(float rating, string surname)
{
    string giveRespectRequest = $"UPDATE Doctors SET Doctors.rating=(Doctors.rating+{rating})/2.0 where Doctors.surname_d = '{surname}';";
    try
    {
        using (connection = new SqlConnection(connectionString))
        {
            SqlCommand giveRespectComm = new SqlCommand(giveRespectRequest, connection); 
            giveRespectComm.ExecuteNonQuery();
        }
    }
    catch (Exception ex)
    {
        connection.Close();
        MessageBox.Show(ex.Tostring());
    }
    finally
    {
        RefreshDGV();
    }
}

catch (Exception ex)
{
    connection.Close();
    MessageBox.Show(ex.Tostring());
}