How to update data from datagridview to database?

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C#

Hi Guys,

I would like to know on how to update data from the datagridview to database. I have two datagridview and two buttons. At form load, Datagridview1 will display all the records from tblAssessment. Then if the user clicked button 1, it will select the top 2 students based from their results. It will then be passed to Datagridview2. the user will saved the data from the datagridview2 to the database. But I got problem in updating the database. How to fix this? Below is my code:

void fillGrid() // loads data from the database to datagridview1
      {
          p_table = new DataTable();
          p_table.Clear();

          m_da = new SqlDataAdapter("Select AssessmentNumber,StudentFirstName,StudentMiddleName,StudentLastName,SchoolYear,GradeLevel,Result from tblSectioning Where GradeLevel='" + label2.Text + "' AND SectionName='" + "Null" + "'", conn);
          m_da.Fill(p_table);
          dataGridView1.DataSource = p_table;
      }


      void sumofall() //sum of all enrolled students
      {

          string query = "SELECT COUNT (*) FROM tblAssessment where GradeLevel ='" + label2.Text +  "'";
          SqlDataAdapter dAdapter = new SqlDataAdapter(query, conn);
          DataTable source = new DataTable();
          dAdapter.Fill(source);
          label7.Text = source.Rows[0][0].ToString();
          loginpage1 frr = new loginpage1();
          frr.numberofstudents = label7.Text;


      }


      private void button1_Click(object sender, EventArgs e) //gets the top 2 in the datagridview1
      {


          for (int i = 0; i <= 4; i++)
          {
              p_table1 = new DataTable();
              p_table1.Clear();
              m_da1 = new SqlDataAdapter("Select Top 2 AssessmentNumber,StudentFirstName,StudentMiddleName,StudentLastName,GradeLevel,Result FROM tblSectioning Where GradeLevel='" + label2.Text + "' ORDER BY Result Desc", conn);

              m_da1.Fill(p_table1);
              dataGridView2.DataSource = p_table1;
          }


      }
      private void button2_Click(object sender, EventArgs e) //updating of data from datagridview 2 to database
      {


              conn = new SqlConnection(connec.GetServer());
              conn.Open();
              cmd = new SqlCommand("update  tblStudentInformation set SectionName='" + textBox1.Text + "', ShiftSched='" + comboBox1.SelectedItem + "' Where  GradeLevel='" + label2.Text + "'", conn);
              m_dr = cmd.ExecuteReader();
              conn.Close();
              m_dr.Close();


              conn = new SqlConnection(connec.GetServer());
              conn.Open();
              cmd1 = new SqlCommand("update  tblClass set SectionName='" + textBox1.Text + "', ShiftSched='" + comboBox1.SelectedItem + "' Where  GradeLevel='" + label2.Text + "'", conn);
              m_dr1 = cmd1.ExecuteReader();
              conn.Close();
              m_dr1.Close();
              MessageBox.Show("Record Updated");

              dataGridView2.ClearSelection();
              fillGrid();


      }