Mysql improve SELECT speed

Question

I\'m currently trying to improve the speed of SELECTS for a MySQL table and would appreciate any suggestions on ways to improve it.

We have over 300 million records

Answer 1

I would do two things - first throw some indexes on there around tag and date as suggested above:

alter table table add index (tag, date);

Next break your query into a main query and sub-select in which you are narrowing your results down when you get into your main query:

SELECT date, value
FROM table
WHERE date BETWEEN 'x' and 'y'
AND tag IN ( SELECT tag FROM table WHERE tag = 'a' )
ORDER BY date