sql - 林克；如何执行多个条件的左外连接？

Question

我正在尝试模仿:

DB1 AS A LEFT OUTER JOIN
DB2 AS B 
ON A.[Currency Code] = B.[Currency Code] 
AND A.[Document Date] >= B.[Starting Date] 
AND A.[Document Date] <= B.[Ending Date]

这是我现在拥有的:

from ledgers in ledgerEntries
join currency in currencyExchange
    on ledgers.CurrencyCode equals currency.CurrencyCode
        into c
from currencies in c.DefaultIfEmpty()
where
    ledgers.DocumentDate >= currencies.StartingDate
    && ledgers.DocumentDate <= currencies.EndingDate

我读过有关创建匿名类型并将它们设置为彼此相等的信息，但是当使用小于和大于来比较日期时这不起作用。

Answer 1

好像this答案正是我要找的。

from ledgers in ledgerEntries
join currency in currencyExchange
    on ledgers.CurrencyCode equals currency.CurrencyCode
        into c
from currencies in c.Where(currency => currency.StartingDate <= ledgers.DocumentDate 
&& currency.EndingDate <= ledgers.DocumentDate).DefaultIfEmpty()

结合this回答，我能够简化为:

from ledgers in ledgerEntries
from currencies in currencyExchange.Where(
    currency => currency.CurrencyCode == ledgers.CurrencyCode
    && currency.StartingDate <= ledgers.DocumentDate 
    && currency.EndingDate <= ledgers.DocumentDate).DefaultIfEmpty()