How to group database tables using Group By - php

Question

I am developing a simple php shopping cart site which connected to a databse named products and has tables Orders,user,products. The orders table has the following fields :
OrderId , product_id , user_id , quantity ... When the user orders for example 3 products . The data is inserted from SESSION['cart'] Below is the query
$query = "insert into orders (product_id,user_id,Quantity) values ('$key','$id','$value')";
mysql_query($query);
Now the problem is if user orders more than one product, three orderID's are generated, because he ordered 3 products and each orderId refers to that product. When i use the select statement it shows all the orders of the users but i want to group them, So that if person ordered more than 1 products at a time, the list would show me single orderID but all the products with the user who ordered it. Below is the image of database table record from orders table and the select query i am using ..
OrderId product_id user_id Quantity
1 4 1 1
3 21 1 3
4 19 1 1
5 21 1 3
6 19 1 2
$sql1=mysql_query("SELECT * FROM orders,USER WHERE user.`user_id`=orders.`user_id`");
while($row = mysql_fetch_array($sql1))
{
$sReturn .='
<tr>
<td>' . $row['user_id'] . '</td>
<td>' . $row['OrderId'] . '</td>
<td>' . $row['product_id'] . '</td>
<td>' . $row['Quantity'] . '</td>
</tr>';
}
What select query can be used someone told me groupby with sum ..

Answer 1

this will get u the sum of products by each user according to product_id
Updated
SELECT SUM( orders.Quantity ) , COUNT( orders.order_id ) , orders.user_id
FROM orders join user on (user.`user_id`=orders.`user_id`)
GROUP BY orders.user_id

Answer 2

You need to add a table called something like OrderItem or OrderRow where you put the product information for each order. Fields could be OrderID, ProductID, Quantity, ItemPrice.
It's a good idea to store the price you told the customer at the time of ordering, otherwise you will get a lot of problems when changing prices in the future.

Answer 3

You need to fix your order_id - it cant be autoincrement. Then this is what I think you are asking.
select order_id, sum(quantity)
from orders
group by order_id
I have left the where clause out as I dont know what filter you will want on it.

Answer 4

SELECT * FROM user_table WHERE id =
(SELECT user_id FROM order_table WHERE order_id = n limit 1);
But much better if you will create separate table for order which containing order info and table for linking an order and a products (id, order_id, product_id, quantity).

Answer 5

I have figured out the query .. below is the query for getting number of orders + Quantity or Number OF Products + user_id ...
SELECT user.`user_id`,SUM(quantity) AS Number_Of_Products,COUNT(Orders.OrderID) AS NumberOfOrders FROM Orders
LEFT JOIN USER
ON Orders.user_id=user.`user_id`
GROUP BY username;
below is the output
user_id Number_Of_Products NumberOfOrders
1 10 5