SQL Sub_query 和联合

Posted 2023-05-09

【中文标题】SQL Sub_query 和联合

【英文标题】：SQL Sub_query and joint

【发布时间】：2021-03-23 09:05:26

【问题描述】：

使用子查询来确定犯罪次数最多的社区区域名称？

我这几天一直在尝试解决这个问题，但我遇到了一个完整的问题

请大家帮帮我吧！

select community_area_name, community_area_number 
from CHICAGO_PUBLIC_SCHOOLS 
where community_area_number in (select community_area_number 
                                from CHICAGO_CRIME_DATA 
                                where community_area_number = '25');

select community_area_number, community_area_name 
from CHICAGO_PUBLIC_SCHOOLS 
where community_area_number in (select community_area_number 
                                from CHICAGO_CRIME_DATA);

【问题讨论】：

请看：Why should I provide an MCRE for what seems to me to be a very simple SQL query?

try exists select community_area_number, community_area_name from CHICAGO_PUBLIC_SCHOOLS a where exists(select '' from CHICAGO_CRIME_DATA b where a.community_area_number =b.community_area_number )

在一个有类似问题的班级中，如果我们有相同的信息，您的问题不会是您试图从 CHICAGO_PUBLIC_SCHOOLS 表而不是 CENSUS_DATA 表中提取信息吗？

【参考方案1】：

我假设你想要这样的东西：

select cps.community_area_number, cps.community_area_name 
from CHICAGO_PUBLIC_SCHOOLS cps
where cps.community_area_number = (select ccd.community_area_number 
                                   from CHICAGO_CRIME_DATA ccd
                                   order by ccd.num_crimes desc 
                                   limit 1
                                  ) ccd;

我不知道犯罪数量是如何确定的，所以我做了一个专栏。

请注意，如果存在平局，则返回任意区域。

【参考方案2】：

我相信你可以试试这样的：

%%sql 
SELECT COMMUNITY_AREA_NAME, COMMUNITY_AREA_NUMBER AS MOST_CRIMES FROM CENSUS_DATA
WHERE COMMUNITY_AREA_NUMBER IN (SELECT COUNT(COMMUNITY_AREA_NUMBER) FROM CRIME_DATA GROUP BY COMMUNITY_AREA_NUMBER) ;

【参考方案3】：

    %%sql select community_area_name 
    from CENSUS_DATA 
    where community_area_number = (select A.community_area_number from CHICAGO_CRIME_DATA as A 
    GROUP BY A.community_area_number 
    ORDER BY COUNT (A.community_area_number) DESC LIMIT 1)

【参考方案4】：

试试这个：

select COMMUNITY_AREA_NUMBER, COMMUNITY_AREA_NAME FROM ChicagoCensusData WHERE COMMUNITY_AREA_NUMBER IN (SELECT TOP 2 COMMUNITY_AREA_NUMBER FROM ChicagoCrimeData GROUP BY COMMUNITY_AREA_NUMBER ORDER BY COUNT(*) DESC);

我使用了前 2 个原因，第一个原因是大多数犯罪没有 community_area_number