I’ve recently switched from SQLite3 to PostGreSQL and came across the following error this morning:

my_app_development=> select category from codes;
ERROR:  column "category" does not exist
LINE 1: select category from codes;

The following post solved the issues in one sentence:

http://archives.postgresql.org/pgsql-novice/2007-01/msg00032.php

Yes. In postgres, unquoted column and table names are converted to lower case.

The user also added that when using PostGreSql you should either be always, or never using quotes around column names.