ช่วยดูโค๊ด ดึงข้อมูลจาก SQL Server มาใส่ใน DataGridView แล้วเช็คข้อมูลซ้ำ

private void button1_Click(object sender, EventArgs e)
        {
            if (dataGridView1.Rows.Count != 0)
            {

                for (int q = 0; q < dataGridView1.Rows.Count; q++)
                {

                    if (dataGridView1.Rows[q].Cells[q].Value.ToString() == textBox1.Text)//ถ้าซ้ำ
                    {
                        MessageBox.Show("abc");
                    }
                    else
                    {
                        string strConn = "Data Source = localhost;" + "Initial Catalog = Books; " + "Integrated Security = SSPI;";
                        SqlConnection conn = new SqlConnection(strConn);
                        if (conn.State == ConnectionState.Closed)
                        {
                            conn.Open();
                        }
                        else
                        {
                            conn.Close();
                            conn.Open();
                        }
                        SqlCommand cmd = conn.CreateCommand();
                        string sqlstatement = "select * from Books where idb='" + textBox1.Text + "'";
                        cmd.CommandType = CommandType.Text;
                        cmd.CommandText = sqlstatement;
                        SqlDataReader reader = cmd.ExecuteReader();

                        if (reader.HasRows)
                        {
                            int i = 0, j = 1, l = 2;
                            while (reader.Read())
                            {

                                string idb = reader[0].ToString();
                                string names = reader[1].ToString();
                                string price = reader[2].ToString();
                                double to = Convert.ToInt32(price);
                                double per = (to * 10) / 100;

                                dataGridView1.Rows.Add();

                                dataGridView1.Rows[k].Cells[i].Value = idb;
                                dataGridView1.Rows[k].Cells[j].Value = names;
                                dataGridView1.Rows[k].Cells[l].Value = price;
                                i++;
                                j++;
                                l++;
                                k++;
                            }
                        }
                        else
                        {
                            MessageBox.Show("!!!ไม่มีรหัสหนังสือนี้!!!", "ข้อมูล", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        }
                        conn.Close();
                    }
                    }
                }


                
        }