Question

如何从下表国家/地区列出表面积大于同一地区所有其他国家/地区的所有国家/地区的名称：

+----------------------------------------------+---------------------------+-------------+
| name                                         | region                    | surfacearea |
+----------------------------------------------+---------------------------+-------------+
| Aruba                                        | Caribbean                 |      193.00 |
| Afghanistan                                  | Southern and Central Asia |   652090.00 |
| Angola                                       | Central Africa            |  1246700.00 |
| Anguilla                                     | Caribbean                 |       96.00 |
| Albania                                      | Southern Europe           |    28748.00 |
| Andorra                                      | Southern Europe           |      468.00 |
| Netherlands Antilles                         | Caribbean                 |      800.00 |

到目前为止，我已经提供了此代码，但这并没有列出国家/地区？这段代码是否正确？

select region, max(surfacearea) as maxArea 
from country 
group by region;

Answer 1

可以使用临时表的内连接

 select name from 
 country  as a
 inner  join      
 ( select region, max(surfacearea) as maxarea 
 from country 
 group by region ) as t    on a.region = t.region    
 where a.surfacearea =  t.maxarea;

Answer 2

看起来你的查询确定了最大的＆＃34;每个区域的表面区域的价值。要获取国家/地区，您可以将查询结果再次加入国家/地区表格，以获取与地区和地区相匹配的国家/地区。

 SELECT c.*
   FROM ( -- largest surfacearea for each region
          SELECT n.region
               , MAX(n.surfacearea) AS max_area
            FROM country n 
           GROUP BY n.region
        ) m
   JOIN country c
     ON c.region      = m.region 
    AND c.surfacearea = m.max_area

Answer 3

您可以在WHERE IN转化中使用原始查询：

select *
from country
where (region, surfacearea) in (
  select region, max(surfacearea) as maxArea 
  from country 
  group by region
)

sqlfiddle

其他方式：

select c1.*
from country c1
left join country c2
  on  c2.region = c1.region
  and c2.surfacearea > c1.surfacearea
where c2.region is null;

select c1.*
from country c1
where not exists (
  select *
  from country c2
  where c2.region = c1.region
    and c2.surfacearea > c1.surfacearea
);

sqlfiddle

基于特定SQL组的列表

3 个答案: