Question

我可以获得按section_mod_id

分组的最高totalColumns数量

查询

SELECT 
    day_id, section_mod_id, count(day_id) as totalColumns 
FROM 
    `supervision` sup
INNER JOIN   
    `section_mod` s ON sup.section = s.section_mod_id
GROUP BY 
    day_id, section_mod_id 
ORDER BY 
    (s.section_mod_id) ASC

例如

day_id  section_mod_id totalColumns
-----------------------------------
127          2             3
103          2             1
23           2             2
105          2             1
23           6             1

到这个

day_id  section_mod_id totalColumns
-----------------------------------
127          2             3 
23           6             1

仅返回每个部分的最高编号

是否可以使用mysql数据库？

Answer 1

在大多数数据库中，您可以使用ANSI标准row_number()函数：

SELECT sm.*
FROM (SELECT day_id, section_mod_id, count(*) as totalColumns,
             ROW_NUMBER() OVER (PARTITION BY section_mod_id ORDER BY count(*) DESC) as seqnum
      FROM supervision s INNER JOIN
           section_mod m ON s.section = m.section_mod_id
      GROUP BY day_id, section_mod_id 
     ) sm
WHERE seqnum = 1;

在MySQL中，最简单的方法可能是这个技巧：

SELECT SUBSTRING_INDEX(GROUP_CONCAT(day_id ORDER BY totalColumns DESC), ',', 1) as day_id,
       section_mod_id, MAX(totalColumns)
FROM (SELECT day_id, section_mod_id, count(*) as totalColumns
      FROM supervision s INNER JOIN
           section_mod m ON s.section = m.section_mod_id
      GROUP BY day_id, section_mod_id 
     ) sm
WHERE seqnum = 1
GROUP BY section_mod_id

Answer 2

使用子查询尝试以下内容。

注意：您可以使用临时表作为内部子查询。

    select day_id,section_mod_id,totalColumns from 
    (
    select t1.day_id ,t1.section_mod_id,t1.totalColumns
    ,count(*) as rowNumber 
    from        
         (SELECT  day_id, section_mod_id, count(day_id) as totalColumns FROM supervision sup
           INNER JOIN section_mod s ON sup.section = s.section_mod_id  GROUP BY day_id, section_mod_id 
         ) t1
          inner join 
         (SELECT  day_id, section_mod_id, count(day_id) as totalColumns FROM supervision sup
           INNER JOIN section_mod s ON sup.section = s.section_mod_id  GROUP BY day_id, section_mod_id 
         )t2 
       on t1.section_mod_id=t2.section_mod_id
       and t1.totalColumns<=t2.totalColumns
    group by t1.day_id, t1.section_mod_id,t1.totalColumns
    ) t where rowNumber=1

查询返回每行的最大数字

2 个答案: