PostgreSQL - “DISTINCT ON” and “GROUP BY” syntax

Question

I realized that a database query was returning unexpected results do to my improper use of \"DISTINCT ON\" and \"GROUP BY\"

I\'m hoping someone can set me straight on th

Answer 1

It is probably not the best way of dealing with this but you can try using window function:

SELECT DISTINCT object_id, MAX(event_timestamp)
OVER (PARTITION BY object_id)  
FROM test_select ORDER BY max DESC;

From the other hand it works as well:

SELECT object_id, MAX(event_timestamp) as max_event_timestamp
FROM test_select 
GROUP BY object_id 
ORDER BY max_event_timestamp DESC;