LINQ的左连接、右连接、内连接

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
};

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,
                 };