How can I get the percentage of total rows with mysql for a group?

Question

below I have a query that will get the most common user agents for a site from a table of user agents and a linked table of ip addresses:

SELECT count(*) as          


        

Answer 1

If you add with rollup after your group by clause, then you will get a row where string is NULL and num is the total of all the browsers. You can then use that number to generate percentages.

I can't really imagine a single query doing the calculation and being more efficient than using with rollup.

Answer 2

Yes you can:

select num, string, 100 * num / total as percent
from (
    select count(*) as num, string
    from useragent_ip
    left join useragents on useragent_id = useragents.id
    group by useragent_id) x
cross join (
    select count(*) as total
    from useragent_ip
    left join useragents on useragent_id = useragents.id) y
order by num desc, string;

I removed the having num > 2, because it didn't seem to make sense.