Brett Mc Bride <brett.mcbr...@deakin.edu.au> wrote: > My understanding of UNION ALL is that it won't sort the rows...? > [...]
It doesn't, but that's not promised for every data set, ev- ery PostgreSQL version, every phase of the moon. To quote <URI:http://www.postgresql.org/docs/8.4/interactive/queries-union.html>: | UNION effectively appends the result of query2 to the result | of query1 (although there is no guarantee that this is the ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | order in which the rows are actually returned). Furthermore, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | it eliminates duplicate rows from its result, in the same | way as DISTINCT, unless UNION ALL is used. SQL deals with (unordered) sets, and therefore any use of "LIMIT" without "ORDER BY" indicates a bug waiting to bite you when you least expect it. Tim -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
