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

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

SELECT * FROM (
    SELECT *,if(@last_method=method,0,1) as new_method_group,@last_method:=method 
    FROM rpc_responses 
    ORDER BY method,timestamp DESC
) as t1
WHERE new_method_group=1;

Given that you want one resulting row per method this solution should work, using mysql variables to avoid a JOIN.

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

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