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Asked: 2026-06-15T19:48:31+00:00

I would really like to better understand what is involved in creating a UDF

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I would really like to better understand what is involved in creating a UDF that operates over windows in PostgreSQL. I did some searching about how to create UDFs in general, but haven’t found an example of how to do one that operates over a window.

To that end I am hoping that someone would be willing to share code for how to write a UDF (can be in C, pl/SQL or any of the procedural languages supported by PostgreSQL) that calculates the running average of numbers in a window. I realize there are ways to do this by applying the standard average aggregate function with the windowing syntax (rows between syntax I believe), I am simply asking for this functionality because I think it makes a good simple example. Also, I think if there was a windowing version of average function then the database could keep a running sum and observation count and wouldn’t sum up almost identical sets of rows at each iteration.

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  1. Editorial Team

    You have to look to postgresql source code postgresql/src/backend/utils/adt/windowfuncs.c and postgresql/src/backend/executor/nodeWindowAgg.c

    There are no good documentation 🙁 — fully functional window function should be implemented only in C or PL/v8 – there are no API for other languages.

    http://www.pgcon.org/2009/schedule/track/Version%208.4/128.en.html presentation from author of implementation in PostgreSQL.

    I found only one non core implementation – http://api.pgxn.org/src/kmeans/kmeans-1.1.0/

    http://pgxn.org/dist/plv8/1.3.0/doc/plv8.html

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