var results = from c in db.Companies
              join cn in db.Countries on c.CountryID equals cn.ID
              join ct in db.Cities on c.CityID equals ct.ID
              join sect in db.Sectors on c.SectorID equals sect.ID
              where (c.CountryID == cn.ID) && (c.CityID == ct.ID) && (c.SectorID == company.SectorID) && (company.SectorID == sect.ID)
              select new { country = cn.Name, city = ct.Name, c.ID, c.Name, c.Address1, c.Address2, c.Address3, c.CountryID, c.CityID, c.Region, c.PostCode, c.Telephone, c.Website, c.SectorID, Status = (ContactStatus)c.StatusID, sector = sect.Name };


return results.ToList();

var Data= (from dealer in Dealer join dealercontact in DealerContact on dealer.ID equals dealercontact.DealerID
select new{
dealer.Id,
dealercontact.ContactName

}).ToList();

因为我更喜欢表达式链语法，下面是你如何做到这一点:

var dealerContracts = DealerContact.Join(Dealer, 
                                 contact => contact.DealerId,
                                 dealer => dealer.DealerId,
                                 (contact, dealer) => contact);

实际上，在linq中，通常最好不要加入。当有导航属性时，一个非常简洁的方式来写你的linq语句是:

from dealer in db.Dealers
from contact in dealer.DealerContacts
select new { whatever you need from dealer or contact }

它转换为where子句:

SELECT <columns>
FROM Dealer, DealerContact
WHERE Dealer.DealerID = DealerContact.DealerID

它是这样的:

from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}

为了更好的示例，最好为您的表提供合理的名称和字段。：）

更新

我认为对于你的疑问，这可能更合适:

var dealercontacts = from contact in DealerContact
                     join dealer in Dealer on contact.DealerId equals dealer.ID
                     select contact;

既然你要找的是联系人，而不是经销商。

基本上LINQ连接操作符对SQL没有好处。例如，下面的查询

var r = from dealer in db.Dealers
   from contact in db.DealerContact
   where dealer.DealerID == contact.DealerID
   select dealerContact;

将导致内部连接在SQL

join对IEnumerable<>有用，因为它更有效:

from contact in db.DealerContact  

条款将对每个经销商重新执行 但对于IQueryable<>则不是这样。另外，连接也不太灵活。