LINQ的左连接、右连接、内连接

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本文详细介绍了LINQ中三种主要的连接查询方式：左连接、右连接和内连接的使用方法及示例代码。通过具体实例，展示了如何在C#中实现不同类型的连接操作，以满足复杂的数据关联需求。

https://www.cnblogs.com/shiningrise/p/5571471.html

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,
                 };