How to make a table of exchange rates?

Question

Database design

Here, for example, a dollar costs some euros, some rubles, but what is the dollar valued against?
So I need to make a table of currencies, how can I make that single constant, against which I will calculate all currencies?
Or should I take this information from the CBR website?

Answer 1

It is quite logical that the exchange rate is the ratio of one currency to another. so what does it mean against what the dollar is valued? What you evaluate is what you evaluate.
in base it is possible to store the most banal relation
1 | USD | 35 |
I don’t think it will be a lot of work to calculate RUR )
10 rubles = (10 * 1) / 35
10 dollars = (10 * 35) / 1