Optimizing percentage calculation SQL query

Question

I have a table like this:

------------------
sl no | Error type
------------------
1     | err1
------------------
2     | err2
------------------
3     | err1
------------------
4     | err2
------------------
5     | err2
------------------
6     | err3
------------------

Result I want:

---------------------------
Error type | Count | %
---------------------------
err1       | 2     | 33.33
---------------------------
err2       | 3     | 50
---------------------------
err3       | 1     | 16.66
---------------------------

I'm using following query to get above result:

select 
    error as Error,
    count(*) as Count, 
    100* count(*)/(select count(*) from logs) as Percentage 
from logs 
group by error;

Is it optimized for the task? If not, what are some other efficient ways I can get that information?

Answer 1

This query will perform the count(*) per row. I'd query it once, and cross join it to the individual counts:

SELECT     a.error, a.cnt, 100 * a.cnt / b.total_count AS percentage
FROM       (SELECT   error, COUNT(*) as cnt
            FROM     logs
            GROUP BY error) a
CROSS JOIN (SELECT COUNT(*) AS total_count FROM logs) b