问题
Forgive my ignorance on this question, as I don't have much experience in this area. I have a page that uses a mysql COUNT(*) query to return a user's stats. For example, something like:
SELECT COUNT(*) FROM worker WHERE worker_id = '1234';
It uses the index for worker_id and checking out the EXPLAIN seems that the query looks good. However, this performs absolutely brutally, and can take 5+ seconds for a single query on a table with a million+ rows. Additionally, this is quite a common query, and sometimes it will result in a mysql timeout error with multiple queries trying to run this.
What would be a good way to 'solve' this issue? The information changes quite rapidly so I don't think caching it would work. How would I go about fixing this, and what do some large sites do the show stats (for example, Facebook Friends or Twitter Followers)?
回答1:
First, be sure that you have an index on worker(worker_id).
Second, if the column is really a number and not a string, then don't use single quotes:
SELECT COUNT(*)
FROM worker
WHERE worker_id = 1234;
Third, if you just need to know if the worker exists (and don't actually need the count), then run a query like this:
select 1
from worker
where worker_id = 1234
limit 1;
And check to see if any rows are returned.
来源：https://stackoverflow.com/questions/28705668/way-to-improve-or-eliminate-a-mysql-count