Niceql
This is a small, nice, simple and dependentless solution for SQL prettifiyng for Ruby. It can be used in an irb console without any dependencies ( run ./console from bin and look for examples ).
Any reasonable suggestions on formatting/coloring are welcome
Before/After
SQL prettifier:

PG errors prettifier
before:

after:

Installation
Add this line to your application's Gemfile:
gem 'niceql'
And then execute:
$ bundle
Or install it yourself as:
$ gem install niceql
Usage
With ActiveRecord
# puts colorized ( or not if you are willing so ) to_niceql ( you need to call puts otherwise to_niceql looks ugly )
Model.scope.niceql
# only formatting without colorization can run as a SQL query in connection.execute
Model.scope.to_niceql
# prettify PG errors
Model.scope_with_err.explain_err
Without ActiveRecord
puts Niceql::Prettifier.prettify_sql("SELECT * FROM ( VALUES(1), (2) ) AS tmp")
# see colors in irb %)
#=> SELECT *
#=> FROM ( VALUES(1), (2) ) AS tmp
# rails combines err with query, so don't forget to do it yourself
# to get real nice result you should executeprettified version (i.e. execute( prettified_sql ) !) of query on your DB!
# otherwise you will not get such a nice output
puts Niceql::Prettifier.prettify_pg_err(<<-ERR )
ERROR: VALUES in FROM must have an alias
LINE 2: FROM ( VALUES(1), (2) )
^
HINT: For example, FROM (VALUES ...) [AS] foo.
SELECT err
FROM ( VALUES(1), (2) )
ORDER BY 1
ERR
# ERROR: VALUES in FROM must have an alias
# LINE 2: FROM ( VALUES(1), (2) )
# ^
# HINT: For example, FROM (VALUES ...) [AS] foo.
# SELECT err
# FROM ( VALUES(1), (2) )
# ^
# ORDER BY 1
Limitations
Right now gem detects only uppercased form of verbs with very simple indentation and parsing options.
Customizing colors
If your console support more colors or different schemes, or if you prefer different colorization, then you can override ColorizeString methods. Current colors are selected with dark and white console themes in mind, so a niceql colorization works good for dark, and good enough for white.
Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/alekseyl/niceql.
License
The gem is available as open source under the terms of the MIT License.