----- Original Message -----
From: Peter Brawley <peter.brawley@stripped>
To: Sebastiaan van Erk <sebster@stripped>
Sent: Monday, November 13, 2006 10:43:26 AM GMT-0500 US/Eastern
Subject: Re: How do I do this query efficiently?
Right, if you want the value column you need too, you need a different
SELECT t1.id, t1.version, t1.value
FROM data t1
LEFT JOIN data t2 ON t1.id=t2.id AND t1.version < t2.version
WHERE t2.id IS NULL;
Sebastiaan van Erk wrote:
> Thanks for your quick answer, but unfortunately this query does not
> return the "value" column of the row; and that is the column I am
> ultimately interested in (in combination with the id).
> Peter Brawley wrote:
>> >for every "id" I want exactly one row, namely the row with the
>> maximum value of "version".
>> SELECT id,MAX(version) FROM data GROUP BY id;
>> Sebastiaan van Erk wrote:
>>> Hi all,
>>> I have the following simple table:
>>> CREATE TABLE data (
>>> id int NOT NULL,
>>> version int NOT NULL,
>>> value int NOT NULL,
>>> PRIMARY KEY (id, version)
>>> ENGINE=InnoDB DEFAULT CHARSET=utf8;
>>> What I would like to do is to find all the values for the latest
>>> versions, that is, for every "id" I want exactly one row, namely the
>>> row with the maximum value of "version". Without using SQL I can
>>> think of a very efficient way for the query optimizer to accomplish
>>> this for me, namely by using the primary key to iterate through each
>>> value for "id" and then looking for the maximum "version", which is
>>> essentialy O(1) because it's the last entry in the index for that
>>> specific id. However, I don't know how to do this query in SQL, the
>>> closest I got was:
>>> select id, version, value from data d1 where version = (select
>>> max(d2.version) from data d2 where d2.id = d1.id)
>>> However this is extremely inefficient and takes much to long (in the
>>> order of 5 seconds on the data I have).
>>> Does anybody know an efficient way to do this?
>>> Thanks in advance,
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