1、左连接：var LeftJoin = from emp in ListOfEmployeesjoin dept in ListOfDepartmenton emp.DeptID equals dept.ID into JoinedEmpDeptfrom dept in JoinedEmpDept.DefaultIfEmpty()select new                        {EmployeeName = emp.Name,DepartmentName = dept != null ? dept.Name : null                        }; 2、右连接：var RightJoin = from dept in ListOfDepartmentjoin employee in ListOfEmployeeson dept.ID equals employee.DeptID into joinDeptEmpfrom 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,                 };