How to find sales per hour between two date - mysql

Question

Suppose I have 5 records for a sales table.
ID Name datetime_col
1 ABC 2016-09-15 02:07:56
2 HSJ 2016-09-31 11:45:45
3 JSD 2016-11-26 07:09:56
4 JUH 2016-12-31 12:00:00
5 IGY 2017-01-13 14:00:07
I want to find how many records are there in sales table for each hour between 2016-09-15 AND 2017-01-13
Then result should be like
Hour sales_at_this_hour
2016-09-15 01:00:00 0
2016-09-15 02:00:00 1
2016-09-15 03:00:00 0
...
...
2017-01-13 01:00:00 0
2017-01-13 02:00:00 0
2017-01-13 03:00:00 0
....
2017-01-13 14:00:00 1
Then find the average of sales_at_this_hour using MySQL

Answer 1

EDIT: sorry not fully understand the question at first.
Use DATE_FORMAT
select
DATE_FORMAT(datetime_col, '%Y-%m-%d %h:00:00') as date,
count(id) as count
from table_name
group by date;
Get result with hours that has sales_at_this_hour > 1 (not exactly what you ask for)
datetime_col count
2016-02-04 05:00:00 5
2016-02-04 07:00:00 1
2016-02-04 08:00:00 5
2016-02-04 10:00:00 10
2016-02-04 11:00:00 1
Provide start_date and end_date, and then use DATEDIFF to calculate total time interval for the average calculation.
set #start_date = '2016-01-01', #end_date = '2017-01-01';
select
DATE_FORMAT(group_by_date.datetime, '%h:00:00') as hour,
AVG(group_by_date.count) / DATEDIFF(#end_date, #start_date) as average
from (
select
DATE_FORMAT(created_dtm, '%Y-%m-%d %h:00:00') as datetime,
count(id) as count
from table_name
where created_dtm > #start_date
and created_dtm < #end_date
group by datetime
) group_by_date
group by hour;
For each hour,
average sale count per day = total sale count / total days
hour average
01:00:00 0.03841209
02:00:00 0.01653005
03:00:00 0.0306716
04:00:00 0.01147541
05:00:00 0.01179831