Question

driver [ dcode, dname ]
route [ rcode, departure,arrival ]
ride [ dcode, rcode ]

SELECT dname FROM driver WHERE dcode IN (
   SELECT dcode FROM ride WHERE rcode IN (
       SELECT rcode FROM route WHERE departure = 'Barcelona' AND arrival = 'Madrid'
   ) AND
   rcode IN (
       SELECT rcode FROM route WHERE departure = 'Madrid' AND arrival= 'Barcelona'
   )
);

关于制作两条路线的司机：马德里 - 巴塞罗那和巴塞罗那 - 马德里，但我的查询不起作用。

Answer 1

你的内部查询（第二个lvl）没有返回任何结果，因为可能不存在rcode，它可以在第一个子集（B-> M）中，而在第二个子集中（M-> B）。请试试这个：

SELECT dname FROM driver WHERE dcode in
(SELECT dcode 
 FROM ride JOIN route
 ON (ride.rcode=route.rcode)
 WHERE route.departure = 'Barcelona' AND route.arrival = 'Madrid'
) AND dcode in (
 SELECT dcode 
 FROM ride JOIN route
 ON (ride.rcode=route.rcode)
 WHERE route.departure = 'Madrid' AND route.arrival = 'Barcelona'
)

Answer 2

我认为您采取的方法是：

获取巴塞罗那到马德里的路线上的dcode司机。我们称之为 Set1 。
获取马德里到巴塞罗那的司机dcode。我们称之为 Set2 。
最后，为dname同时包含 Set1 和 Set2 的驱动程序获取dcode。

您对 Set1 的查询是：

SELECT dcode FROM ride WHERE rcode IN (
   SELECT rcode FROM route WHERE departure = 'Barcelona' AND arrival = 'Madrid'
)

在同一行， Set2 的查询将是：

SELECT dcode FROM ride WHERE rcode IN (
   SELECT rcode FROM route WHERE departure = 'Madrid' AND arrival = 'Barcelona'
)

最后，您需要{/ 1}} Set1 ＆amp; Set2 。这将转换为查询：

dcode

在您的查询中，您不是在两组中查找SELECT dname FROM driver WHERE dcode IN ( SELECT dcode FROM ride WHERE rcode IN ( SELECT rcode FROM route WHERE departure = 'Barcelona' AND arrival = 'Madrid' ) ) AND dcode IN ( SELECT dcode FROM ride WHERE rcode IN ( SELECT rcode FROM route WHERE departure = 'Madrid' AND arrival = 'Barcelona' ) )，而是在两组中查找dcode。

改进建议：对于获取rcode集的查询，您可以使用内部联接而不是使用嵌套查询。例：

dcode

Answer 3

不应该是

    SELECT dname FROM driver WHERE dcode IN (
    SELECT dcode FROM ride WHERE rcode IN (
        SELECT rcode FROM route WHERE departure = 'Barcelona' AND arrival =    
'Madrid'
     ) OR
   rcode IN (
       SELECT rcode FROM route WHERE departure = 'Madrid' AND arrival= 'Barcelona'
   )
);

OR代替AND ...？

MySQL：双重IN（）语句

3 个答案: