sql - PostgreSQL incorrect sorting

Question

I use PostgreSQL 9.3.3 and I have a table with one column named as title (character varying(50)).

When I have executed the following query:

select * from test
order by title asc

I got the following results:

#
A
#Example

Why "#Example" is in the last position? In my opinion "#Example" should be in the second position.

Answer 1

Sort behaviour for text (including char and varchar as well as the text type) depends on the current collation of your locale.

See previous closely related questions:

• PostgreSQL Sort
• https://stackoverflow.com/q/21006868/398670

If you want to do a simplistic sort by ASCII value, rather than a properly localized sort following your local language rules, you can use the COLLATE clause

select * 
from test
order by title COLLATE "C" ASC

or change the database collation globally (requires dump and reload, or full reindex). On my Fedora 19 Linux system, I get the following results:

regress=> SHOW lc_collate;
 lc_collate  
-------------
 en_US.UTF-8
(1 row)

regress=> WITH v(title) AS (VALUES ('#a'), ('a'), ('#'), ('a#a'), ('a#')) 
          SELECT title FROM v ORDER BY title ASC;
 title 
-------
 #
 a
 #a
 a#
 a#a
(5 rows)

regress=> WITH v(title) AS (VALUES ('#a'), ('a'), ('#'), ('a#a'), ('a#')) 
          SELECT title FROM v ORDER BY title COLLATE "C" ASC;
 title 
-------
 #
 #a
 a
 a#
 a#a
(5 rows)

PostgreSQL uses your operating system's collation support, so it's possible for results to vary slightly from host OS to host OS. In particular, at least some versions of Mac OS X have significantly broken unicode collation handling.