Corey Tisdale <corey@xxxxxxxxxxxxxxxx> writes: > SELECT > meaningful_data, > event_type, > event_date > FROM > event_log > GROUP BY > event_type > ORDER BY > event_date DESC Is event_type a primary key, or at least a candidate key, for this table? (I would guess not based on the name.) If it is, then the above is actually well-defined, because there is only one possible input row for each group. The GROUP BY is actually kinda pointless in that case. If it is not, then the above is *not* well-defined --- there are multiple possible meaningful_data and event_date values for each event_type value, and you have absolutely no idea which ones you will get. This is not allowed per SQL standard, and MySQL has done you no service by failing to detect the ambiguity. What you might be after is something like Postgres' DISTINCT ON feature, which allows you to resolve the ambiguity by specifying a sort order for the rows within each group (and then taking the first row in each group). See the "weather reports" example in our SELECT reference page. I have never really played around with this aspect of MySQL ... but looking at this example, and presuming that you find that it actually does something useful, I wonder whether they interpret the combination of GROUP BY and ambiguous-per-spec ORDER BY in some fashion similar to DISTINCT ON. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
