Exactly Tom, I see no fundamental problem for it not to be implemented, since comparison operator is already implemented. In fact, MIN/MAX should work for all types for which comparison operator is defined.
Regarding index support, there should not be an issue if the index is defined for the record (e.g. `CREATE INDEX ON my_table(ROW(field_a, field_b))`). However such indexes seem not to be supported. Whether a composite index is compatible with a record created on the indexed fields in every edge case I'm not sure... Alexander, rewriting the year-month example is easy, but how would you rewrite this query? CREATE TABLE events(event_time TIMESTAMP, message VARCHAR, user_id VARCHAR); You want a newest message for each user. It's easy with MAX(record): SELECT user_id, MAX(ROW(event_time, message)).message FROM events GROUP BY user_id; One option is to rewrite to a subquery with LIMIT 1 SELECT user_id, (SELECT message FROM events e2 WHERE e1.user_id=e2.user_id ORDER BY event_time DESC LIMIT 1) FROM events e1 GROUP BY user_id; If your query already has multiple levels of grouping, multiple joins, UNIONs etc., it gets much more complex. I also wonder if the optimizer would pick the same plan as it would be if the MAX(record) is supported. Viliam On Fri, Mar 22, 2024 at 4:12 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > Aleksander Alekseev <aleksan...@timescale.com> writes: > >> In my queries I often need to do MIN/MAX for tuples, for example: > >> SELECT MAX(row(year, month)) > >> FROM (VALUES(2025, 1), (2024,2)) x(year, month); > >> This query throws: > >> ERROR: function max(record) does not exist > >> Was this ever discussed or is there something preventing the > implementation? > > > I believe it would be challenging to implement max(record) that would > > work reasonably well in a general case. > > As long as you define it as "works the same way record comparison > does", ie base it on record_cmp(), I don't think it would be much > more than a finger exercise [*]. And why would you want it to act > any differently from record_cmp()? Those semantics have been > established for a long time. > > regards, tom lane > > [*] Although conceivably there are some challenges in getting > record_cmp's caching logic to work in the context of an aggregate. >
