Question

所以我有两个表，STOPS_AT和POINT_OF_INTEREST，它们是这样的：

STOPS_AT [ Route_ID，Stop_ID ]

和

POINT_OF_INTEREST [ Stop_ID，名称，类别]

现在我正在尝试选择在某个兴趣点拥有最多停靠点的Route_ID。换句话说，具有最多停靠次数的路线，也出现在POINT_OF_INTEREST表中。我尝试过以下方法：

select Route_ID
from (select Route_ID, count(POINT_OF_INTEREST.Stop_ID) as cnt
  from STOPS_AT R
  group by Route_ID
 ) rc join
 (select max(cnt) as maxcnt
  from (select Route_ID, count(POINT_OF_INTEREST.Stop_ID) as cnt
        from STOPS_AT
        group by Route_ID
       ) rc
 ) m
 on rc.cnt = m.maxcnt;

然而，这似乎不起作用，说它不知道POINT_OF_INTEREST表？

Answer 1

您的查询未加入point_of_interest表格 - 这就是您收到错误的原因。您正在尝试计算您未选择的字段。

如果您不需要担心关系，一种简单的方法就是使用limit：

select route_id
from (
   select sa.route_id, count(*) cnt
   from stops_at sa
       join point_of_interest poi on sa.route_id = poi.route_id
   group by sa.route_id
) t
order by cnt desc
limit 1

如果关系是关系，那么您可以使用上面的内容更改您的查询：

select Route_ID
from (
       select sa.route_id, count(*) cnt
       from stops_at sa
           join point_of_interest poi on sa.route_id = poi.route_id
       group by sa.route_id
 ) rc join
 (select max(cnt) as maxcnt
  from (
           select sa.route_id, count(*) cnt
           from stops_at sa
               join point_of_interest poi on sa.route_id = poi.route_id
           group by sa.route_id
       ) rc
 ) m
 on rc.cnt = m.maxcnt;

SQL - 尝试查找两个表之间的最大计数

1 个答案: