MySql Query Grouping by Time

问题

I am trying to create a report to understand the time-of-day that orders are being placed, so I need to sum and group them by time. For example, I would like a sum of all orders placed between 1 and 1:59, then the next row listing the sum of all orders between 2:00 and 2:59, etc. The field is a datetime variable, but for the life me I haven't been able to find the right query to do this. Any suggestions sending me down the right path would be greatly appreciated.

Thanks

回答1:

If by luck it is mysql and by sum of orders you mean the number of orders and not the value amount:

select date_format(date_field, '%Y-%m-%d %H') as the_hour, count(*)
from my_table
group by the_hour
order by the_hour

回答2:

This king of grouping (using a calculated field) will certainly not scale over time. If you really need to execute this specific GROUP BY/ORDER BY frequently, you should create an extra field (an UNSIGNED TINYINT field will suffice) storing the hour and place an INDEX on that column.

That is of course if your table is becoming quite big, if it is small (which cannot be stated in mere number of records because it is actually a matter of server configuration and capabilities as well) you won't probably notice much difference in performance.

来源：https://stackoverflow.com/questions/5464887/mysql-query-grouping-by-time