(Hopefully stupid) select question.

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От Fredric Fredricson
Тема (Hopefully stupid) select question.
Дата
Msg-id 4D3D9FC9.3010802@bonetmail.com
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Ответы Re: (Hopefully stupid) select question.
Re: (Hopefully stupid) select question.
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I have been fighting with a select and can find no satisfactory solution.

Simplified version of the problem:

A table that, in reality, log state changes to an object (represented as a row in another table):

CREATE TABLE t (
    id SERIAL UNIQUE,
    ref INTEGER, -- Reference to a row in another table
    someData TEXT,
    inserted DATE DEFAULT CURRENT_TIMESTAMP
) ;
Then we insert multiple rows for each "ref" with different "someData".


Now I want the latest "someData" for each "ref" like:

ref | someData (only latest inserted)
-------------
 1  | 'data1'
 2  | 'data2'
etc...

The best solution I could find depended on the fact that serial is higher for higher dates. I do not like that because if that is true, it is an indirect way to get the data and could possibly, in the future, yield the wrong result if unrelated changes where made or id's reused.

Here is my solution (that depend on the SERIAL):
SELECT x.ref,x.someData
  FROM t as x
  NATURAL JOIN (SELECT ref,max(id) AS id FROM t GROUP BY ref ORDER BY ref) AS y ;

Can somebody come up with a better solution? (without resorting to stored procedures and other performance killers).

/Fredric
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