Question

我有两个访问表，我需要根据公共列（dest）和表B中最接近表A的时间进行连接。

航班（表A）

ID | dest | land
1  | SUN  | 1/1/2017 8:52:00 AM
2  | SEA  | 1/1/2017 4:39:00 AM

天气（表B）

ID | dest | time                | vis 
1  | SUN  | 1/1/2017 8:15:00 AM | 10
2  | SUN  | 1/1/2017 8:35:00 AM | 5
3  | SUN  | 1/1/2017 8:55:00 AM | 2
4  | SEA  | 1/1/2017 2:48:00 AM | 7
5  | SEA  | 1/1/2017 3:52:00 AM | 10
6  | SEA  | 1/1/2017 4:49:00 AM | 2

期望的结果（表C）

ID | dest | land                | time                | vis
1  | SUN  | 1/1/2017 8:52:00 AM | 1/1/2017 8:35:00 AM | 5
2  | SEA  | 1/1/2017 4:39:00 AM | 1/1/2017 3:52:00 AM | 10

我一直坚持如何加入'dest'和最接近的时间。表A包含~25,000行，表B~100,000。

Answer 1

我会这样做：

SELECT Flights.dest, Flights.land, 
(select time from weather 
    where id = (select top 1 id 
                from weather 
                where dest=flights.dest and time <= flights.land 
                order by time desc)) AS [time], 
(select vis from weather 
    where id = (select top 1 id 
                from weather 
                where dest=flights.dest and time <= flights.land 
                order by time desc)) AS vis
FROM Flights;

或者，使用此查询可以获得相同的结果：

SELECT Flights.dest, Flights.land, 
weather.time, weather.vis
FROM Flights INNER JOIN weather ON Flights.dest = weather.dest
WHERE weather.time = (
   select top 1 time 
   from weather 
   where dest=flights.dest and time <= flights.land 
   order by time desc);

访问查询以在最近的时间加入两个表

1 个答案: