How to prevent similar [duplicate] entries in SQL database?

//CHECK IF COMPLETE DUPLICATE
query = "SELECT * FROM TBL_FLAVORS WHERE flavor_name = @flavor_name AND flavor_supplierid = @supplier_id";
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
                        con.Open();

                        using (SqlCommand cmd = new SqlCommand(query, con))
                        {

                            SqlDataReader read;
                            cmd.Parameters.AddWithValue("@flavor_name", txtFlavorName.Text.ToString());
                            cmd.Parameters.AddWithValue("@supplier_id", supplierid);
                            read = cmd.ExecuteReader();
                            if (read.Read())
                            {
                                MessageBox.Show("This flavor for this supplier already exists.");
                                return;
                            }
                            read.Close();
                        }
                    }


//CHECK IF ALMOST SIMILAR
//IF RECORD FOUND, RETURN
//OTHERWISE, PROCEED TO UPDATE/INSERT

                    query = "SELECT * FROM TBL_FLAVORS WHERE (flavor_name LIKE @flavor_name OR flavor_name LIKE @flavor_name2 OR FLAVOR_NAME LIKE @flavor_name3) AND flavor_supplierid = @supplier_id";
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
                        con.Open();
                        
                            using (SqlCommand cmd = new SqlCommand(query, con))
                            {
                            string flavorname = "%" + txtFlavorName.Text.ToString()+ "%";
                            string flavorname2 = "" + txtFlavorName.Text.ToString() + "%";
                            string flavorname3 = "%" + txtFlavorName.Text.ToString() + "";
                            SqlDataReader read;
                                cmd.Parameters.AddWithValue("@flavor_name", flavorname);
                            cmd.Parameters.AddWithValue("@flavor_name2", flavorname2);
                            cmd.Parameters.AddWithValue("@flavor_name3", flavorname3);
                            cmd.Parameters.AddWithValue("@supplier_id", supplierid);
                                read = cmd.ExecuteReader();
                                if (read.Read())
                                {
                                DialogResult dialog = MessageBox.Show("It is possible that this flavor for this supplier already exists. Do you want to continue?", "", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
                                if (dialog == DialogResult.No)
                                {
                                    return;
                                }
                                }
                                read.Close();
                            }
                    }