2 ms·

> with the full table scan being insertion order/sort by rowid I'm not sure that makes sense. As far as I'm aware selecting without sorting has no guaranteed o

• haimez 5y ago
  No guaranteed order, but very typically a predictable order depending on the query plan chosen. If you’re relying on an ordering, you need to specify it in the query. However, the scan order is predictable for a given engine depending on the query plan. If it’s doing an index scan, you’ll get results in index order and if it’s doing a table scan you’ll get it in table storage order (assuming a transactional, single node [edit: also single threaded] OLTP database- this goes out the window when outputs are aggregated across multi node (edit: or multi threaded) scans without an ORDER BY)
  • barrkel 5y ago
    Postgres can do parallel table and index scans. Don't rely on order without explicit order by.
    • haimez 5y ago
      True, I forgot to consider how single node (multi threaded) parallelism can look a lot like multi node parallelism