如下图所示关系型数据,LinQ语句为:

var Query= from a in data.A
where a.admin==传入的用户名&&a.pwd==传入的密码(可以传入一个model实体)
join b in data.B
            on a.bid equals b.id into ab
            from r1 in ab.DefaultIfEmpty()
            join c in data.C
            on r1.cid equals c.id into bc
            from r2 in bc.DefaultIfEmpty()
            join d in data.D
            on r2.did equals d.id into cd
            from r3 in cd.DefaultIfEmpty()

select new
            {

//这里是table A 的id;
                  Id = a.Id,

//这里是table B的Name;
                  Name = r1.Name,
                  PRo = r2.Pro,
                  ipAdd = r3.IpAdd
            };

//转成数组形式;

        var list = Query.ToList();

//list[0].Name即表示整个LinQ查询的结果的第一条数据的table B的Name,以此类推;

注: r1可以.出table B的所有数据...以此类推;

r2==table C;

r3==table D;

=====================================================================================================

 1 1、左连接：
 2 
 3 var LeftJoin = from emp in ListOfEmployees
 4 join dept in ListOfDepartment
 5 on emp.DeptID equals dept.ID into JoinedEmpDept
 6 from dept in JoinedEmpDept.DefaultIfEmpty()
 7 select new                        
 8 {
 9 EmployeeName = emp.Name,
10 DepartmentName = dept != null ? dept.Name : null                        
11 };
12 
13  
14 
15 2、右连接：
16 
17 var RightJoin = from dept in ListOfDepartment
18 join employee in ListOfEmployees
19 on dept.ID equals employee.DeptID into joinDeptEmp
20 from employee in joinDeptEmp.DefaultIfEmpty()
21 select new                          
22 {
23 EmployeeName = employee != null ? employee.Name : null,
24 DepartmentName = dept.Name
25 };
26 
27  
28 
29 3、内连接：
30 
31  var query = from t in entitiy.TB_GCGL_ADA_USER
32                  join p in entitiy.TB_GCGL_ZY_ZYK
33                  on t.ETPRS_CODE equals p.ETPRS_CODE
34 
35                  select new TB_USER_ZYK
36                  {
37                     USER_ID = t.USER_ID,
38                     USER_NAME = t.USER_NAME,
39                     USER_PASSWord = t.USER_PASSWORD,
40 
41                  };