SQL SELECT与大多数用户

Question

用户的产品：

uid int(11) - userid(primary key, auto_increment) 
name varchar(255) 
pass varchar(64) 
created int(11) 

项目：

pid int(11) ..... 
name varchar(150) 
description varchar(255) 
created int(11) 

users_projects：

uid int(11) - user id 
pid int(11) - product id 

如何选择与分配给它的最ussers项目？

sql查询。

Answer 1

你可以使用这样的事情：

select p.pid, 
    p.name, 
    up.TotalUsers 
from projects p 
inner join 
(
    select pid, count(uid) TotalUsers 
    from users_projects 
    group by pid 
) up 
    on p.pid = up.pid 
order by TotalUsers Desc 
-- limit 1 

见SQL Fiddle with Demo

这将返回所有项目的列表，每个项目总用户的数量。如果你想返回的项目将最多的用户，那么你将包括被注释掉的limit 1。

如果你有一个以上的project具有相同数量的用户，那么你可能需要使用类似这样：

select p.pid, 
    p.name, 
    up.TotalUsers 
from projects p 
inner join 
(
    select pid, count(uid) TotalUsers 
    from users_projects 
    group by pid 
) up 
    on p.pid = up.pid 
where totalusers = (select count(*) Total 
        from users_projects 
        group by pid 
        order by total desc 
        limit 1) 

的小提琴

见 SQL Fiddle with Demo

感谢@JW

Answer 2

以下查询将包含多个具有相同用户数且恰好是最多用户数的项目。

SELECT a.name userName, c.name ProjectName 
FROM users a 
     INNER JOIN users_projects b 
      ON a.uid = b.uid 
     INNER JOIN projects c 
      ON b.pid = c.pid 
     INNER JOIN 
     (
      SELECT pid, COUNT(*) totalCount 
      FROM users_projects 
      GROUP BY pid 
      HAVING COUNT(*) = (SELECT COUNT(*) x 
           FROM users_projects 
           GROUP BY pid 
           ORDER BY x DESC 
           LIMIT 1) 
     ) d ON b.pid = d.pid 
ORDER BY a.Name ASC 

• SQLFiddle Demo (with duplicate project)
• SQLFiddle Demo

Answer 3

如果你正在寻找只有一个项目，以下是最快的方法：

select project_id, count(*) as NumUsers 
from user_projects 
group by project_id 
order by count(*) desc 
limit 1 

（我假设“产品“=”项目“）。