Using alias in subquery

Question

I'm running the following query to get the open positions on a portfolio:

SELECT SUM(trades.quantity) as total_quantity, SUM(trades.price) as total_cost, SUM(trades.price)/SUM(trades.quantity) as cost_per_share,           
trades.ticker, tickers.code
FROM (trades)
LEFT JOIN tickers
ON trades.ticker = tickers.id
GROUP BY tickers.code
HAVING total_quantity > 0
ORDER BY tickers.code

I'd like to add an extra column to show the weightening of a position, i.e.:

total_cost/SUM(total_cost) -- Dividing any given position cost by the total cost of the portfolio

Since aliases cannot be used in calculations, I thought I'd need to use a sub-query. I've tried a few things but couldn't make it to work.

Can anyone shed some light on this? Is sub-query the way to go? Is there any other better way to do it?

Answer 1

Not sure on your query (you appear to be doing a GROUP BY on a field from a LEFT JOINed table, which could be null for non found matching rows), but maybe cross join to a subselect to get the total of all prices

SELECT total_quantity, total_cost, cost_per_share, trades.ticker, tickers.code, total_cost/total_of_prices
FROM
(
    SELECT SUM(trades.quantity) as total_quantity, SUM(trades.price) as total_cost, SUM(trades.price)/SUM(trades.quantity) as cost_per_share,           
    trades.ticker, tickers.code
    FROM trades
    LEFT JOIN tickers
    ON trades.ticker = tickers.id
    GROUP BY tickers.code
    HAVING total_quantity > 0
) Sub1
CROSS JOIN
(
    SELECT SUM(price) as total_of_prices 
    FROM trades 
    WHERE quantity > 0
) Sub2
ORDER BY tickers.code