On Wed, 01 Mar 2017 11:12:29 -0500, Tom Lane <t...@sss.pgh.pa.us> wrote:
>This is a great example of "select distinct" being used as a band-aid >over a fundamental misunderstanding of SQL. It's good advice to never use >"distinct" unless you know exactly why your query is generating duplicate >rows in the first place. On that note: I know most people here don't pay much - or any - attention to SQLServer, however there was an interesting article recently regarding significant performance differences between DISTINCT and GROUP BY as used to remove duplicates. https://sqlperformance.com/2017/01/t-sql-queries/surprises-assumptions-group-by-distinct Now I'm wondering if something similar might be lurking in Postgresql? [Yeah, I know - test it and find out! Thing is, the queries used in the article are not simple. Although not explicitly stated, it hints that - at least for SQLServer - a simple case involving a string column is probably insufficient, and complex scenarios are required to produce significant differences. ] I'll get around to doing some testing soon. For now, I am just asking if anyone has ever run into something like this? George -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
