Question

我有一张犯罪数据表。在简化版中，它看起来像这样：

表格标题：

crime_id, neighborhood, offense

表数据：

 - 1, Old Town,  robbery         
 - 2, Bad Town,    theft        
 - 3, Bad Town,    theft         
 - 4, Uptown,    stolen auto

如果我SELECT * FROM mytable WHERE offense ='theft'，则返回Bad Town的结果。但是，我正在排名，所以我真正感兴趣的是：

Old Town: 0  
Bad Town: theft  
Bad Town: theft  
Uptown:   0

如何编写一个SELECT语句来返回存在盗窃的案例，还会返回没有指定攻击条目的邻居？

更新：这是我的实际选择。我在应用p.campbell和Gratzy非常友好地发布到SELECT的解决方案时遇到了问题。如何将CASE语句与COUNT（*）？

一起应用

SELECT 
        cbn.neighborhoods AS neighborhoods, 
        COUNT(*) AS offenses, 
        TRUNCATE(((na.neighborhood_area_in_sq_meters /1000) * 0.000386102159),2) AS sq_miles,  
        ( COUNT(*) / ((na.neighborhood_area_in_sq_meters /1000) * 0.000386102159) ) AS offenses_per_sq_mile 
        FROM 
            wp_crime_by_neighborhood cbn, wp_neighborhood_area  na
        WHERE 
            cbn.offense='theft' 
            AND 
            cbn.neighborhoods = na.neighborhoods
        GROUP BY 
            cbn.neighborhoods 
        ORDER BY 
            offenses_per_sq_mile DESC

Answer 1

试试这个：

SELECT  cbn.neighborhoods AS neighborhoods,  
    CASE WHEN IFNULL(COUNT(*),0) > 0 THEN CONCAT(COUNT(*), ' ', offense)
         ELSE  '0' 
    END AS offenses
    --- ... and the rest of your query

    FROM        wp_crime_by_neighborhood cbn
    INNER JOIN  wp_neighborhood_area  na  
        ON      cbn.neighborhoods = na.neighborhoods 
    WHERE       cbn.offense='theft'                     
    GROUP BY    cbn.neighborhoods  
    --ORDER BY  offenses_per_sq_mile DESC

Answer 2

我认为使用案例陈述应该这样做。

http://dev.mysql.com/doc/refman/5.0/en/case-statement.html

类似

Select neighborhood, 
case offense when 'theft' then offense  else '0' end case 
from table

Answer 3

如果你想进行排名，那么获取Bad Town的盗窃数量不是更好吗？像这样：

select distinct mt.neighborhood, ifnull(total, 0)
from mytable mt
left join (
  select neighborhood, count(*) as total
  from mytable
  where offense = 'theft'
  group by neighborhood
) as t on t.neighborhood = mt.neighborhood

根据您提供的数据，此查询应返回：

Old Town: 0
Bad Town: 2
Uptown: 0

这对我来说排名更有用。您可以轻松地在那里下订单。

需要简单的MySQL SELECT帮助

3 个答案: