Ordering by the difference between two averages

I have a single table called orders. It has 3 fields I care about: price, type, and bid. Bid is an int with either 0 or 1 depending on if the order is to buy or sell something. 1 is buy, 0 is sell.

orders

|typeID  |price |bid|
|1       |10    |0|
|2       |20    |0|
|3       |30    |0|
|4       |50    |0|
|1       |80    |0|
|2       |30    |0|
|3       |50    |0|
|4       |10    |0|
|1       |8     |1|
|2       |7     |1|
|3       |9     |1|
开发者_Go百科

I'm trying to find which 100 distinct types have the largest difference between the average price of buy and sell orders.

I'm not sure how to go about doing this. I know I can order by an average price for either buy or sell orders, but I need to order by the difference between them. I'm using mysql if that matters.

I'm fairly confident that this should work:

SELECT `typeID`, AVG(IF(`bid`, `price`, 0)) AS `average_buy_price`, AVG(IF(`bid`, 0, `price`)) AS `average_sell_price`,
AVG(IF(`bid`, `price`, 0)) - AVG(IF(`bid`, 0, `price`)) AS `difference`
FROM `orders`
GROUP BY `typeID`
LIMIT 100
ORDER BY `difference` DESC;