php - Mysql sort BY number of filled columns -

i'm comparing prices of products 3 different website. have 3 different prices. if website doesn't offer product, price empty.

mysql looks this:

**id | name | price_1 | price_2 | price 3** 

i sort products, available @ 3 websites. products, available @ 1 website.

and can't figure out how approach this!

if empty fields have null value, can use

select * sometable order isnull(price_1) + isnull(price_2) + isnull(price_3) desc; 

but more sensible solution be:

• you have 1 table, contains products
• you have table, contains product's id, price , value indicates website provided price.

benefits:

• you have count(*) entries of product in second table find out on how many listed
• you can change number of websites time without changing table