The problem is, that the order_line table does not have a currency_id column, it only has the accounting_total_currency_id.

The accounting_total_currency_id shows the currency used for the accounting_total
The currency_id (which is missing) would define which currency the total column has.

Example:

The account is from Germany and the currency of this account is by default EUR
Thats's what the accounting_total_currency_id and accounting_total show.

But the order could be in USD or any other currency and that's what is shows in the total column and to say which currency the total of this order line is would we need the currency_id.

Means:
Accounting Total: 93,49 EUR
Total: 100 ?

I can get this information with an api call

"currency":{"id":123,"code":"USD"}