linq to sql 实现左(右)连接,那个方法是对的
var query2 = from tb0 in db.table_0
join tb1 in db.table_1 on table_0.关联键 equals table_1.关联键
into all
from tb2 in all.DefaultIfEmpty()
select new { ... };
下面是另一方法。。。。。。
左连接left outer join,除了满足连接条件的行,还包括左表的所有行。
右连接right outer join,除了满足连接条件的行,还包括右表的所有行。
eg:var q =
from e in db.Employees
join o in db.Orders on e equals o.Employee into ords
select new
{
e.FirstName,
e.LastName,
Order = ords
};
说明:以Employees 左表,Orders右表,Orders 表中为空时,用null值填充。Join的结果重命名 ords,Order是一个集合。
虽然没有left关键字,但是实现的查询结果是一样的。
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直接join是内连接。
------解决方案--------------------
它产生的sql语句是什么呢?
------解决方案--------------------
- C# code
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 }; 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 };