From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
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To: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | median and percentile function implementation |
Date: | 2013-08-26 12:39:57 |
Message-ID: | CAFj8pRBK1VnLJZrmPK4XK5EvXQ1qx46_nvi4DbBKJW2Gv0HWYQ@mail.gmail.com |
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Lists: | pgsql-hackers |
Hello
Three years ago we worked on implementation of median function.
http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com
Can we implement this function now?
There are a few opened questions:
* immutable parameters of aggregate functions
* effective implementation when data are in memory
* effective implementation when data are out of memory
* effective implementation for usage as window function - running median.
Better than before, we can choose between hashing and sorting based
aggregation. But tuplesort implementation is not right for using as window
function. Second issue can be a not possible reusing of tuplesort for more
final functions - median, percentile in one query.
Ideas how to solve this task? Can we move forward in some points?
Regards
Pavel
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