原文地址：http://blog.sina.com.cn/s/blog_46e9573c01014fx2.html

1、左连接：

var LeftJoin = from emp in ListOfEmployees
join dept in ListOfDepartment
on emp.DeptID equals dept.ID into JoinedEmpDept
from dept in JoinedEmpDept.DefaultIfEmpty()
select new                        
{
EmployeeName = emp.Name,
DepartmentName = dept != null ? dept.Name : null                        
};

实例：

var demandList = (from d in dbBusiness.Demand
join t in dbBusiness.Tender
on new {d.DemandId, OrganId = 0} equals new {t.DemandId, t.OrganId} into demandTender
from dt in demandTender.DefaultIfEmpty()
select new UserDemandTender
{
TenderId = dt.TenderId,
UserId = d.UserId,
IsWinTender = dt.IsWinTender,
Status = d.Status,
Title = d.Title,
Budget = d.Budget,
CategoryNo = d.CategoryNo,
VerifyTime = d.VerifyTime,
CreateTime = d.CreateTime,
BrowsePv = d.BrowsePv,
TenderNumber = d.TenderNumber,
DemandId = d.DemandId,
}).Where(demand => demand.UserId == CurrentUserID).ToList();

 

2、右连接：

var RightJoin = from dept in ListOfDepartment
join employee in ListOfEmployees
on dept.ID equals employee.DeptID into joinDeptEmp
from employee in joinDeptEmp.DefaultIfEmpty()
select new                          
{
EmployeeName = employee != null ? employee.Name : null,
DepartmentName = dept.Name
};

 

3、内连接：

 var query = from t in entitiy.TB_GCGL_ADA_USER
                 join p in entitiy.TB_GCGL_ZY_ZYK
                 on t.ETPRS_CODE equals p.ETPRS_CODE

                 select new TB_USER_ZYK
                 {
                    USER_ID = t.USER_ID,
                    USER_NAME = t.USER_NAME,
                    USER_PASSWORD = t.USER_PASSWORD,

                 };