Getting a percentage from MySql with a group by condition, and precision

Question

I was about to ask the MySql list this and remembered about SO.

Running MySql 5.0.85, I need to be as efficient as possible about a few queries. If I could get a little review, I would appreciate it.

I collect data in the millions, and need the top 50 grouped by one field, with a percentage of how much those top 50 occupy.

Here is what I have come up with... 1) I have a feeling I can be more efficient, perhaps with a join 2) How can I get the percentage to be of precision in the hundredths, so * 100.00 ie: .07 becomes 7.00, getting SQL errors if I (percentage * 100)

SELECT user_agent_parsed, user_agent_original, COUNT( user_agent_parsed ) AS thecount, 
    COUNT( * ) / ( SELECT COUNT( * ) FROM agents ) AS percentage
FROM agents
GROUP BY user_agent_parsed
ORDER BY thecount DESC LIMIT 50;

Second issue, once a day I need to archive the result of the above. Any suggestions on how to best to do that? I can schedule with cron, or in my case, launchd, unless someone has a better suggestion.

Would you think that a simple 'SELECT (the above) INTO foo' would suffice?

Answer 1

First Issue:

select count(*) from agents into @AgentCount;

SELECT user_agent_parsed
     , user_agent_original
     , COUNT( user_agent_parsed )  AS thecount
     , COUNT( * ) / ( @AgentCount) AS percentage
 FROM agents
GROUP BY user_agent_parsed
ORDER BY thecount DESC LIMIT 50;