I have a table, lets call it products, that includes 2 columns for price and currency. Its dealing with euros, pounds and dollars.

I want to be able to generate the logic that can sort the table on the price, but by taking into account the currency exchange rates.

So, lets say the PRODUCTS table has the following records:

Price Currency

5 £
1 $
7 €

If you were to simply sort ascending on Price, it would return:

1
5
7

But if we want to return the results ASCending, according to lowest price value first (taking exchange rate into account), it would need to return:

1
7
5

I do have a RATES table stored in SQL, that has this structure:

id from to rate
-------------------
1 eur gbp 0.683
etc

Which has all of the conversion rates for all possibilities stored in it.

Does anyone have any ideas of the type of SQL code that could achieve this?

I had thought the following code would do the job:

SELECT price,currency,CAST((price*rates.rate) AS UNSIGNED) AS priceval
FROM products, rates
WHERE currency=rates.from_code AND
rates.to_code=0
ORDER BY priceval ASC

Where to_code of 0 means EUROS. And matching currency field (in products) to rates.from_code, would match numeric value that represents each currency:

EUR = 0
USD = 1
GBP = 2

But when I execure this code, it just returns 0 for each of the 3 fields. Anyone got any ideas?

If I remove the ORDER BY priceval ASC clause, then I get the result that I want - apart from the fact that its not in the order I need.
But adding this ORDER BY clause, causes the results to be displayed as 0 for all 3 columns in the select..???

I was being a numpty and reading my results incorrectly. The SQL code I posted does work. Its just that I had many records with 0 price in my test data that I forgot about.

So I worked out the solution as:

SELECT price,currency,CAST((price*rates.rate) AS UNSIGNED) AS priceval
FROM products, rates
WHERE currency=rates.from_code AND
rates.to_code=0
ORDER BY priceval ASC

If this helps anyone else with a similar problem, then great.