Torsten Förtsch wrote > Hi, > > assuming I have a query that computes a running sum like this: > > select id, buy_price, sum(buy_price) over (order by id) sum > from fmb > where 202300<=id and id<=202400 > order by id; > > Do I need the ORDER BY clause at the end? Or does the ORDER BY in the > window function already define the order of the result set? It is possible for the final output to be out-of-order e.g. (2, 3, 1) but the running total associated with each row will be correct. IOW, if you were to manually perform an order-by on the result you would get the same result as if you have included the outer (non-window) order-by in the original query. Input: (1, 1), (2, 2), (3, 3) Possible Output: (2, 2, 3), (3, 3, 6), (1, 1, 1) Expected Output: (1,1,1), (2,2,3), (3,3,6) Not Possible: (2, 2, 2), (3,3,5),(1,1,6) If you want the output in a specific order you should specify that order explicitly. By coincidence, with simple queries, you may consistently get the expected results but that is not something to rely upon. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/window-function-and-order-by-tp5784285p5784292.html Sent from the PostgreSQL - general mailing list archive at Nabble.com. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
