How to select the most recent set of dated records from a mysql table

Question

I am storing the response to various rpc calls in a mysql table with the following fields:

Table: rpc_responses

timestamp   (date)
method      (varchar)
id          


        

Answer 1

Use this solution with caution:
it is not guaranteed to work in future versions of mysql
it is not known to work in mariadb 5.5

This can query may perform well, because there are no joins.

SELECT * FROM (
    SELECT timestamp, method, id, response
    FROM rpc_responses
    WHERE 1 # some where clause here
    ORDER BY timestamp DESC
) as t1
GROUP BY method

The "group by", collapses the result set on method, and returns only 1 row per method, the most recent one, because of the ORDER BY timestamp DESC in the inner query.

FYI, PostgreSQL has a way of doing this built into the language:

SELECT DISTINCT ON (method) timestamp, method, id, response
FROM rpc_responses
WHERE 1 # some where clause here
ORDER BY method, timestamp DESC