Detecting column changes in a postgres update trigger

Question

I have a postgres database with several tables that I want to watch for updates on, and if there\'s any updates, I want to fire a \"hey, something changed\" update. This wor

Answer 1

http://www.postgresql.org/docs/9.3/static/plpython-trigger.html

TD["table_name"]

I do exactly the same type of notify, I loop through all of the columns like this:

    for k in TD["new"]:
        if TD["old"][k] != TD["new"][k]:
            changed.append(k)

changed.append(k) builds my notification string. Somewhere else I do a listen, then broadcast the results out pub/sub to web socket clients.

-g

Answer 2

Another way is to exploit JSON/JSONB functions that come in recent versions of PostgreSQL. It has the advantage of working both with anything that can be converted to a JSON object (rows or any other structured data), and you don't even need to know the record type.

See my original StackOverflow post with appropriate examples.

Answer 3

Read up on the hstore extension. In particular you can create a hstore from a row, which means you can do something like:

changes := hstore(NEW) - hstore(OLD);
...pg_notify(... changes::text ...)

That's slightly more information than you wanted (includes new values). You can use akeys(changed) if you just want the keys.