MAX查询的SQL帮助

Question

我有一个名为bbc的国家/地区表(名称,地区,地区,人口,gdp)

我想要一张表格,其中列出了按地区划分的最大(人口最多)国家的地区,名称和人口.到目前为止,我已经尝试过这个:

SELECT region, name, MAX(population)
FROM bbc
GROUP BY region

它给了我一条错误消息:ORA-00979:不是GROUP BY Expression

我试图更改为GROUP BY区域,名称,但它没有给我正确的表格

Answer 1

您可以对以下查询使用分析:

SELECT name, region, population
  FROM (SELECT region, name, population
             , MAX(population) OVER (PARTITION BY region) maxpop
          FROM bbc)
 WHERE population = maxpop;

内联视图为您提供了一个类似于基表的表,以及一个包含该区域最大填充的额外列.您的顶级选择为您提供每个地区最大国家/地区的国家,地区和人口.

举例说明:

SELECT * FROM bbc;

REGION          NAME        POPULATION
--------------- -------     ----------
North America   USA         300000000
North America   Canada      100000000
North America   Mexico       50000000
South America   Brazil       50000000
South America   Argentina    40000000
South America   Venezuela    20000000

添加分析函数:

SELECT region, NAME, population
     , MAX(population) OVER (PARTITION BY region) maxpop
  FROM bbc;

REGION          NAME                POPULATION      MAXPOP
--------------- -------             ----------      ----------
North America   USA                 300000000       300000000
North America   Canada              100000000       300000000
North America   Mexico               50000000       300000000
South America   Brazil               50000000        50000000
South America   Argentina            40000000        50000000
South America   Venezuela            20000000        50000000

然后成品:

NAME    REGION             POPULATION
------- ---------------    -----------
USA     North America       300000000
Brazil  South America        50000000

还有一个编辑.您可以避免使用嵌套选择,但不能避免使用子查询:

SELECT NAME, region, population
  FROM bbc
 WHERE (region, population) IN
       (SELECT region, MAX(population)
          FROM bbc
         group by region);