MySQL：Group By＆amp;计算多个字段

Question

如果我有一个字段，比如project_id，我想要计算出现次数，我会做类似的事情：

select project_id, count(project_id) as count from tbl group by project_id, order by count desc

如果我想计算同一个表中两个字段组合的出现次数，即计算project_id和service_id组合唯一的行数，该怎么办？

所以，我的表中记录如下：

project_id   service_id
1            1
1            2
1            2
1            2
1            2
1            3
1            4
1            4
1            4


I would want the result of my query to be something like:

project_id   service_id   count
1            1            1
1            2            4
1            3            1
1            4            3

Answer 1

select project_id, service_id, count(*) as count 
from tbl group by project_id, service_id
order by count(*) desc

只需将service_id添加到您的group by和select列表中即可。应该这样做。

编辑 -

根据@Rajah的评论，您的预期输出似乎需要使用

order by project_id asc, service_id asc