select Currencies.Name, Currencies.Sign ,a.ActualPrice
from Currencies
outer apply (select CurrencyID,ActualPrice from Prices
where ProductID=5 and      Currencies.ID=Prices.CurrencyID)a

from c in Currencies
from p in Prices.DefaultIfEmpty()
where p.ProductID.Equals(5) && c.ID==p.CurrencyID
select new {c.Name, p.ActualPrice}

var result =
    Currencies.Select(c => new
                      {
                          Name = c.Name,
                          Sign = c.Sign,
                          ActualPrice = Prices.Where(p => p.ProductID == 5 &&
                                                          p.CurrencyID == c.ID)
                                              .FirstOrDefault()
                      });