What is correct join query?

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SQL

C#3.5

i made physiotherapy management system and i have two tables patient_mstr and old_patient. i give contact_no as primary key and foreign key. i want to search contact no and display particular fields records from table. the code as given below.

What I have tried:

private void txtscrcno_KeyDown(object sender, KeyEventArgs e)
        {
            try
            {
                if (e.KeyCode == Keys.Enter)
                {
                    OleDbCommand cmd = new OleDbCommand("select patient_mstr.Sr_no,patient_mstr.P_name,patient_mstr.M_name,patient_mstr.L_name,old_patient.E_date,patient_mstr.Address,old_patient.Pain,old_patient.Total_charge,old_patient.Total_paid from patient_mstr join on old_patient where patient_mstr.Contact_no=old_patient.Contact_no and Contact_no=@Contact_no", cn);
                    cmd.Parameters.Add(new OleDbParameter("@Contact_no", txtscrcno.Text));
                    cn.Open();
                    if (cmd.ExecuteNonQuery() > 1)
                    {
                        //OleDbDataAdapter da = new OleDbDataAdapter(cmd);
                        OleDbDataAdapter da = new OleDbDataAdapter(cmd);
                        DataSet ds = new DataSet();
                        da.Fill(ds, "patient_mstr");
                        dgvinfo.DataSource = ds;
                        dgvinfo.DataMember = "patient_mstr";
                        cn.Close();
                    }
                    else
                    {
                        MessageBox.Show("There is no record found.","No record",MessageBoxButtons.OKCancel,MessageBoxIcon.Error);
                    }
                }
            }
            catch (Exception j)
            {
                MessageBox.Show(j.Message);
            }
        }