Mysql database huge records

Question

I have a database table which contain 100M records. I have a query that is taking 20 minutes to run - how can I make it simple and fast?

SELECT newnum,
       Sum(Ceil(seconds / 60)) AS ttime
FROM   astb
GROUP BY newnum
ORDER  BY ttime DESC 
LIMIT 100;

Answer 1

ORDER BY and LIMIT work best with indexes. So if possible you could have indexes on column newnum .

Another point is you are making a calculation every single record in a huge table. I strongly recommend to select records in a temp table first than make your calculation on those records.

EDIT UPDATED SCRIPT: You could use temp table like this:

CREATE TEMPORARY TABLE temp AS 
(SELECT newnum, SUM(seconds) AS ttime 
FROM astb GROUP BY newnum)

SELECT newnum, CEIL(ttime / 60) AS ttime
FROM temp
ORDER  BY ttime DESC 
LIMIT 100;

DROP TABLE temp;

Answer 2

这不是很好的数据库设计，但是您可以添加一列来保存ceil(seconds/60) ，所以您不必一直重新计算它吗？