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copied!<p>My version uses a joint of the table MyObjects against a subset of itself, created by a subquery, and containing only the last generation for each object:</p> <pre><code>SELECT O.id,generation,value FROM MyObjects O, (SELECT id,max(generation) AS max_generation FROM MyObjects WHERE generation <= $GENERATION_ID GROUP BY id) AS TheMax WHERE TheMax.max_generation = generation AND O.deleted is False ORDER BY generation DESC; </code></pre> <p>In the above query, the GENERATION_ID is hardwired. A way to parametrize it is to write a function:</p> <pre><code>CREATE OR REPLACE FUNCTION generation_objects(INTEGER) RETURNS SETOF MyObjects AS 'SELECT O.id,generation,value,deleted FROM MyObjects O, (SELECT id,max(generation) AS max_generation FROM MyObjects WHERE generation <= $1 GROUP BY id) AS TheMax WHERE TheMax.max_generation = generation AND O.deleted is False;' LANGUAGE SQL; </code></pre> <p>Now, it works. With this table:</p> <pre><code>> SELECT * FROM MyObjects; id | generation | value | deleted ----+------------+-------+--------- 1 | 1 | 99 | f 2 | 2 | 88 | f 1 | 3 | 77 | f 2 | 4 | 88 | t 3 | 5 | 33 | f 4 | 6 | 22 | f 3 | 7 | 11 | f 2 | 8 | 11 | f </code></pre> <p>I get:</p> <pre><code>> SELECT * FROM generation_objects(1) ORDER by generation DESC; id | generation | value | deleted ----+------------+-------+--------- 1 | 1 | 99 | f > SELECT * FROM generation_objects(2) ORDER by generation DESC; id | generation | value | deleted ----+------------+-------+--------- 2 | 2 | 88 | f 1 | 1 | 99 | f > SELECT * FROM generation_objects(3) ORDER by generation DESC; id | generation | value | deleted ----+------------+-------+--------- 1 | 3 | 77 | f 2 | 2 | 88 | f </code></pre> <p>And then, at the following generation, object 2 is deleted:</p> <pre><code>> SELECT * FROM generation_objects(4) ORDER by generation DESC; id | generation | value | deleted ----+------------+-------+--------- 1 | 3 | 77 | f </code></pre>

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