Query result organization

I am trying to figure out the most efficient way to format this query.

I have three tables - Transaction, Purchase and Item.

The desired result is to select sales data (quantity/sales total) for each item for a specific client.

the tables are formatted as follows: (=primary key)*

Transaction: Transaction_ID*, Timestamp

Purchase: Purchase_ID*, Sale, Item_ID, Transaction_ID, Quantity

Item: Item_ID*, Client_ID, Description

As of right now I have a query set up to select each item for a given client_id:

SELECT Item_ID, Description FROM Item WHERE Client_ID = $ClientId  

Then I store the results in an array, and executing a query to retrieve the sales data for each Item_ID between a given date-range:

SELECT Sale, Quantity
  FROM Purchase INNER JOIN Transaction
    ON Purchase.Transaction_ID = Transaction.Transaction_ID
 WHERE Transaction.Timestamp >= $start
   AND Transaction.Timestamp<= $end

Then for each row fetched, I sum the quantity.

It gets the job done, but is probably not the most efficient way to get this done.

I would like to order this data by the sales totals, putting the greatest number first

How would you go about sorting this from greates开发者_JAVA百科t to least?

Is there a way to get this all done in one query?

would the following work?

SELECT Item_ID, SUM(Quantity), Sum(Sale)
FROM Item
JOIN Purchase ON Item.Item_ID=Purchase.Item_ID
JOIN Transaction ON Purchase.Transaction_ID=Transaction.Transaction_ID
WHERE Client_ID = $ClientId
AND Transaction.Timestamp>= $start
AND Transaction.Timestamp <= $end
GROUP BY Item_ID
ORDER BY SUM(Quantity), SUM(Sale) DESC

I think this is what you want from the good question you asked. There's probably a stupid mistake in there somewhere as I haven't tested it on your tables, but it ought to get you started.