On Mon, Feb 5, 2024 at 7:23 AM Sean v <sean@xxxxxxxxxxxxxx> wrote:
This is related to a question I asked on dbs.stackexchange.com: https://dba.stackexchange.com/questions/335501/why-doesnt-postgres-apply-limit-on-groups-when-retrieving-n-results-per-groupBut to reiterate - I have a query like this:SELECT "orders".*
FROM "orders"
WHERE (user_id IN ?, ?, ?)
ORDER BY "orders"."created_at" LIMIT 50
[snip]
So my question is twofold:- why doesn't Postgres use the composite index, and then retrieve only the minimum necessary amount of rows (50 per user) using the query I posted above?
But your query does not list the first 50 rows per user. It only returns the first 50 rows of:
SELECT "orders".*
FROM "orders"
WHERE (user_id IN ?, ?, ?)
ORDER BY "orders"."created_at"
Who knows which users are going to be in that list???
