Question

这在MySQL上应该很简单，但我很困惑为什么SQL Server 2008会这样做是不可能的。

SELECT * FROM Customers AS cust
LEFT JOIN (SELECT TOP 1 * FROM Vehicles AS v WHERE v.CustNo=cust.CustNo) AS veh ON veh.CustNo=cust.CustNo;

错误是

The multi-part identifier "cust.CustNo" could not be bound.

任何想法的人？

Answer 1

这是查询：

SELECT *
FROM Customers cust LEFT JOIN
     (SELECT TOP 1 *
      FROM Vehicles v
      WHERE v.CustNo = cust.CustNo
     ) veh
     ON veh.CustNo = cust.CustNo;

我不知道任何允许子查询中的关联子句的数据库。您可以使用OUTER APPLY完成此操作：

SELECT *
FROM Customers cust OUTER APPLY
     (SELECT TOP 1 *
      FROM Vehicles v
      WHERE v.CustNo = cust.CustNo
     ) veh;

Answer 2

以下是使用row_number()的一种方法：

select * 
from (
    SELECT *, row_number() over (partition by cust.custno order by v.custno) rn 
    FROM Customers cust
        LEFT JOIN Vehicles v ON v.CustNo=cust.CustNo
) t
where rn = 1

SQL SERVER：左连接和子查询

2 个答案: