Usage of group by

sql Execution order in statement :

from-> where -> join ->  group by -> having ->select ->order by ->limit

group by after ,

select Statements can write only three fields

1）group by Field of

2） Aggregate functions sum count...

3) Constant values

for example ： The wrong way to write ,brand,model Property cannot be queried

select
mid_id,
brand,
model,
count(*) login
from dwd_start_log
group by mid_id;

correct ：

select
mid_id,
brand,
model,
count(*) login
from dwd_start_log
group by mid_id,brand,model;