查询帮助使用COUNT和JOIN需要

Question

我正在寻找帮助编写MYSQL查询.我有两个表,一个叫做用户,另一个叫做切换.users表具有以下结构:

uid
first_name
last_name

和切换表:

uid (references user table)
switch_number
reg_date

切换表有多个uid值,我希望生成一个包含以下输出的表:

uid | switches

其中switch指的是切换表中出现的次数.有人可以指导我如何使用MySQL和PHP做到这一点.我感谢任何帮助.

问候,

Answer 1

这将输出表中uid找到的s switched及其计数

select uid, count(switch_number) as switches
from switched
group by uid

如果你也需要零计数那么

select u.uid, count(s.switch_number) as switches
from users u
left join switched s on s.uid = u.uid
group by u.uid