linq之多表连接分分快三全天计划网站

作者:分分快三全天计划网站

1、左连接:

 

2、右连接:

3、内连接:

1、左连接:

3、内连接:

 

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 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

                 };

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,          //重点
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

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 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                        
};

select new TB_USER_ZYK 

USER_ID = t.USER_ID, 
USER_NAME = t.USER_NAME, 
USER_PASSWORD = t.USER_PASSWORD,

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
};

1、左连接:

};

                 };

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

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,

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
};

如果想实现右连接,就把两个表换一下位置。

 

 

 

 左链接或右链接,使用DefaultIfEmpty()语法,采用些语法前需要用到into语法

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