เพิ่มสินค้า ถ้ามี product_id เหมือนกัน ไห้นำค่าที่จะเพิ่ม กับค่าใน database มา + กัน

object maxid_product_id = new SqlCommand("select product_id from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar();
                        object maxid_receive_details = new SqlCommand("select receive_id from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar();// maxid
                        object maxid_receive_details2 = new SqlCommand("select id from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar();// maxid_receive_details2                       
                        object remark = new SqlCommand("select remark from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar(); //remark
                        object maxid_unit_num = new SqlCommand("select product_unit_num from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar();//maxid_unit_num                                           
                        int maxid_unit_num_x = Convert.ToInt32(maxid_unit_num);

                        object balance = new SqlCommand("update stock_onhands set quantity = quantity+'" + maxid_unit_num_x + "' where product_id= 'quantity' ", conn).ExecuteScalar();
                        

                        //////maxid_product_id = new SqlCommand("select product_id from receive_details where id=(select max(id) from receive_details)", conn).ExecuteScalar();
                        //object maxbalance = new SqlCommand("select isnull(quantity,'0') from stock_onhands where id=(select max(product_id) from stock_onhands)", conn).ExecuteScalar();//balance                       
                        //int maxid_unit_num_x = Convert.ToInt32(maxid_unit_num);
                        //int maxbalance_y = Convert.ToInt32(maxbalance);
                        //int balance = maxid_unit_num_x + maxbalance_y;

                       

                        SqlCommand scm1 = new SqlCommand(
        "INSERT INTO stock_incomings (receive_id, receive_detail_id, product_id,quantity,balance, remark) values('" + maxid_receive_details + "','" + maxid_receive_details2 + "','" + maxid_product_id + "','" + maxid_unit_num + "','" + balance + "','" + remark + "') "
                        , conn);

                        scm1.ExecuteNonQuery();

                        int store_id = 1;
                        SqlCommand scm2 = new SqlCommand(
                        "insert into stock_onhands (product_id,store_id,quantity) values ('" + maxid_product_id + "','" + store_id + "','" + balance + "')"
                            , conn);
                        scm2.ExecuteNonQuery();

DataTable dt = new DataTable();
            dt.Load(new SqlCommand("select * from receive_details where id=(select max(id) from receive_details)", conn).ExecuteReader());
            DataRow dr = dt.Rows[0];

MessageBox.Show(dr[1].ToString());

SqlCommand scm2 = new SqlCommand(
                        "UPDATE  stock_onhands SET product_id =" + maxid_product_id + ",store_id = "store_id,quantity =" + balance" , conn);
                        scm2.ExecuteNonQuery();

Datatable dt;
dt=Connection.Execute(" select * from tablename where product_id='xxxxx' ");

if (dt.RowCount==0)
{
// Insert Data
}
else
{
//Update Data
}

DataTable dt = new DataTable();
            dt.Load(new SqlCommand("select * from tablename where product_id='xxxxx' ", conn).ExecuteReader());
            DataRow dr = dt.Rows[0];

DataTable dt = new DataTable();
                        dt.Load(new SqlCommand("select * from stock_onhands where product_id='' ", conn).ExecuteReader());

                        if (dt.Rows.Count == 0)
                        {
                            int store_id = 1;
                            SqlCommand scm12 = new SqlCommand(
                            "insert into stock_onhands (product_id,store_id,quantity) values ('" + maxid_product_id + "','" + store_id + "','" + balance + "')"
                                , conn);
                            scm12.ExecuteNonQuery();
                        }
                        else
                        {
                            int store_id = 1;
                            SqlCommand scm11 = new SqlCommand(
                            "UPDATE  stock_onhands SET product_id =" + maxid_product_id + ",store_id = " + store_id + ",quantity =" + balance + " ", conn);
                            scm11.ExecuteNonQuery();
                        }

 SqlDataAdapter sda = new SqlDataAdapter(
"select id, private_code, product_code, serial,name, unit_name, description, remark, add_date FROM products INNER JOIN stock_onhands ON products.id=stock_onhands.product_id ", conn);
            

 SqlDataAdapter sda = new SqlDataAdapter(
"select id, private_code, product_code, serial,name, unit_name, description, remark, add_date FROM (products INNER JOIN stock_onhands ON products.id=stock_onhands.product_id) ", conn);

SqlDataAdapter sda = new SqlDataAdapter(
            "select * FROM products INNER JOIN stock_onhands ON products.id=stock_onhands.product_id", conn);