Question

For example, if I have to count the comments belonging to an article, it’s obvious I don’t need to cache the comments total.

But what if I want to paginate a gallery (WHERE status = 1) containing 1 million photos. Should I save that in a table called counts or SELECT count(id) as total every time is fine?

Are there other solutions?

Please advise. Thanks.

Answer 1

For MySQL, you don’t need to store the counts, you can use SQL_CALC_FOUND_ROWS to avoid two queries.

E.g.,

SELECT SQL_CALC_FOUND_ROWS * 
FROM Gallery
WHERE status = 1
LIMIT 10;
SELECT FOUND_ROWS();

From the manual:

In some cases, it is desirable to know how many rows the statement
would have returned without the LIMIT, but without running the
statement again. To obtain this row count, include a
SQL_CALC_FOUND_ROWS option in the SELECT statement, and then invoke
FOUND_ROWS() afterward.

Sample usage here.