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          (varchar) response    (mediumtext)  PRIMARY KEY(timestamp,method,id) 

What is the best method of selecting the most recent responses for all existing combinations of method and id?

• For each date there can only be one response for a given method/id.

• Not all call combinations are necessarily present for a given date.

• There are dozens of methods, thousands of ids and at least 365 different dates

Sample data:

timestamp  method  id response 2009-01-10 getThud 16 '.....' 2009-01-10 getFoo  12 '.....' 2009-01-10 getBar  12 '.....' 2009-01-11 getFoo  12 '.....' 2009-01-11 getBar  16 '.....' 

Desired result:

2009-01-10 getThud 16 '.....' 2009-01-10 getBar 12 '.....' 2009-01-11 getFoo 12 '.....' 2009-01-11 getBar 16 '.....' 

(I don’t think this is the same question – it won’t give me the most recent response)

Answer 1

Self answered, but I’m not sure that it will be an efficient enough solution as the table grows:

SELECT timestamp,method,id,response FROM rpc_responses  INNER JOIN (SELECT max(timestamp) as timestamp,method,id FROM rpc_responses GROUP BY method,id) latest USING (timestamp,method,id);