Question

如何在linq中使用此查询。 EmployeeID是另一个表。

select * 
from Employees where EmployeeID  
in  (select ID from EmployeeIDs where ID between 3 and 7)

Answer 1

var result= (
        from e in db.Employees
        where
            (
                from eId in db.EmployeeIDs
                where eId.ID>=3 && eId.ID<=7
                select eId.ID
            ).Contains(e.EmployeeID)
        select e
    );

其中db是linq数据上下文

或者您也可以这样做：

var result= db.Employees.Where(a=>a.EmployeeID>=3 && a.EmployeeID<=7);

或者您也可以这样做：

var result= (
            from e in db.Employees
            where
                (
                    from eId in db.EmployeeIDs
                    where eId.ID>=3 && eId.ID<=7
                    && e.EmployeeID==eId.ID
                    select eId.ID
                ).Any()
            select e
        );

Answer 2

听起来像是想要加入：

var query = from emp in employees
            join empId in employeeIds.Where(x => x.ID >= 3 && x.Id <= 7)
              on emp.EmployeeID equals empID
            select emp;

如果你真的需要两张桌子的话。另一方面，如果您可以假设任何employeeIds employee.ID中始终存在有效ID，那么您可以使用：

var query = employees.Where(x => x.EmployeeID >= 3 && x.EmployeeID <= 7);

Answer 3

即使在SQL中，SELECT语句中嵌套的IN也是多余的。

你可以写

SELECT * 
FROM  Employees 
WHERE EmployeeID Between 3 and 7

在SQL中Between 3 AND 7只是Column >= 3 and Column <= 7

的语法糖

因此，您可以针对您的EF上下文编写以下内容。

var results = from e in context.Employees
              where EmployeeId >= 3 && EmployeeId <= 7
              select e;

Answer 4

使用联接非常简短直接;

from emp in db.Employees
join eid in db.EmployeeIDs on emp.EmployeeID equals eid.ID
where emp.EmployeeID >= 3 && emp.EmployeeID <= 7
select emp

这也将导致非常理智且直接的SQL，而没有嵌套选择（为了便于阅读而编辑）

SELECT *
FROM Employees AS emp
INNER JOIN EmployeeIDs AS eid ON emp.EmployeeID = eid.ID
WHERE (emp.EmployeeID >= 3) AND (emp.EmployeeID <= 7)

选择使用linq

4 个答案: