Proper way to access latest row for each individual identifier?

Question

I have a table core_message in Postgres, with millions of rows that looks like this (simplified):

┌────────────────┬──         


        

Answer 1

Another approach using ROW_NUMBER(), which is widely supported across RDBMS:

SELECT * 
FROM (
    SELECT 
        c.*,
        ROW_NUMBER() OVER(PARTITION BY mmsi ORDER BY time DESC) rn
    FROM core_message c
) AS cr WHERE rn = 1

This query should benefit of existing index core_messag_mmsi_b36d69_idx.