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

问题

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)

回答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

回答2:

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),method,id FROM rpc_responses GROUP BY method,id) latest
USING (timestamp,method,id);

回答3:

Try this...

SELECT o1.id, o1.timestamp, o1.method, o1.response   
FROM rpc_responses o1
WHERE o1.timestamp = ( SELECT max(o2.timestamp)
                       FROM rpc_responses o2
                       WHERE o1.id = o2.id )
ORDER BY o1.timestamp, o1.method, o1.response

...it even works in Access!

回答4:

i used this,worked for me

select max(timestamp),method,id from tables where 1 group by method,id order by timestamp desc

回答5:

Subquery is very taxing when the data set becomes larger.

Try this:

SELECT t1.* 
FROM rpc_responses AS t1 
INNER JOIN rpc_responses AS t2 
GROUP BY t1.method, t1.id, t1.timestamp
HAVING t1.timestamp=MAX(t2.timestamp)    
ORDER BY t1.timestamp, t1.method, t1.response;

回答6:

The concept of "most recent" is fairly vague. If you mean something like the 100 most recent rows then you can just add a TOP(100) to your SELECT clause.

If you mean the "most recent" based on a the most recent date then you can just do

SELECT timestamp,method,id,response 
FROM rpc_responses
HAVING max(timestamp) = timestamp

回答7:

...is more than one year later but i might help someone To select all the queries starting from latest

SELECT *
FROM rpc_responses
ORDER BY timestamp DESC

来源：https://stackoverflow.com/questions/435703/how-to-select-the-most-recent-set-of-dated-records-from-a-mysql-table

标签

mysql

sql

date

greatest-n-per-group