You can use analytic functions
SELECT *
FROM (SELECT c.*,
rank() over (partition by user_id order by ts desc) rnk
FROM comments c)
WHERE rnk = 1
Depending on how you want to handle ties (if there can be two rows with the same user_id
and ts
), you may want to use the row_number
or dense_rank
function rather than rank
. rank
would allow multiple rows to be first if there was a tie. row_number
would arbitrarily return one row if there was a tie. dense_rank
would behave like rank
for the rows that tied for first but would consider the next row to be second rather than third assuming two rows tie for first.