Hi, On 22 September 2011 21:32, Rohan Malhotra <yourbuddyrohan@xxxxxxxxx> wrote: > Hi Gurus, > What is difference between > select * from items order by random() limit 5; > and > select * items limit 5; > my basic requirement is to get random rows from a table, my where clause This one says: give me first five rows which you have around. Usually rows are from cache and you can get the same result after each execution. On the other hand the first query returns different result set every time. If you know approximate number of rows in "items" table then you can use this (and avoid sort): select * from items where random() < 5.0 / total_rows limit 5 You can replace total_rows by this query: select reltuples from pg_class where relname = 'items' (ie select * from items where random > 5.0 / (select reltuples from pg_class where relname = 'items') limit 5) -- Ondrej Ivanic (ondrej.ivanic@xxxxxxxxx) -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
