ATTENTION: After ver 0.5.0 the ActiveRecord integration is provided via standalone gem: rails_sql_prettifier!

This is a small, nice, simple and zero dependency solution for SQL prettifying for Ruby. It can be used in an irb console without any dependencies ( run bin/console and look for examples ).

Any reasonable suggestions are welcome.

Please pay attention: even though issue is resolved still potentially UPDATE or INSERT request might corrupt your data, please don't patch pg_adapter on production!


SQL prettifier:

alt text

PG errors prettifier

before: alt text

after: alt text


Add this line to your application's Gemfile:

gem 'niceql'

And then execute:

$ bundle
# if you are using rails, you may want to install niceql config:
rails g niceql:install 

Or install it yourself as:

$ gem install niceql


Niceql.configure do |c|
  # Setting pg_adapter_with_nicesql to true will force formatting SQL queries
  # before execution. Formatted SQL will lead to much better SQL-query debugging and much more clearer error messages 
  # if you are using Postgresql as a data source.  
  # Adjusting pg_adapter in production is strongly discouraged! 
  # If you need to debug SQL queries in production use exec_niceql
  # default: false
  # uncomment next string to enable in development
  # c.pg_adapter_with_nicesql = Rails.env.development?

  # uncomment next string if you want to log prettified SQL inside ActiveRecord logging. 
  # default: false
  # c.prettify_active_record_log_output = true

  # Error prettifying is also configurable
  # default: defined? ::ActiveRecord::Base && ActiveRecord::Base.configurations[Rails.env]['adapter'] == 'postgresql'
  # c.prettify_pg_errors = defined? ::ActiveRecord::Base && ActiveRecord::Base.configurations[Rails.env]['adapter'] == 'postgresql'

  # spaces count for one indentation
  c.indentation_base = 2

  # setting open_bracket_is_newliner to true will start opening brackets '(' with nested subqueries from new line 
  # i.e. SELECT * FROM ( SELECT * FROM tags ) tags; will transform to: 
  # SELECT * 
  # FROM 
  # ( 
 #    SELECT * FROM tags 
 #  ) tags; 
 # when open_bracket_is_newliner is false: 
  # SELECT * 
  # FROM ( 
 #   SELECT * FROM tags 
 # ) tags; 
 # default: false
  c.open_bracket_is_newliner = false


With ActiveRecord ( you need rails_sql_prettifier for that! )

  # puts colorized and formatted corresponding SQL query

  # only formatting without colorization, you can run output of to_niceql as a SQL query in connection.execute  

  # prettify PG errors if scope runs with any 

Without ActiveRecord

    puts Niceql::Prettifier.prettify_sql("SELECT * FROM ( VALUES(1), (2) ) AS tmp")
    #=>  SELECT * 
    #=>  FROM ( VALUES(1), (2) ) AS tmp

    puts Niceql::Prettifier.prettify_multiple("SELECT * FROM ( VALUES(1), (2) ) AS tmp; SELECT * FROM table")

    #=>  SELECT * 
    #=>  FROM ( VALUES(1), (2) ) AS tmp;
    #=>  SELECT * 
    #=>  FROM table

   puts Niceql::Prettifier.prettify_pg_err( pg_err_output, sql_query )

   # to get real nice result you should execute prettified version (i.e. execute( prettified_sql ) !) of query on your DB! 
   # otherwise you will not get such a nice output
    raw_sql = <<~SQL
     SELECT err 
     FROM ( VALUES(1), (2) )
     ORDER BY 1

    puts Niceql::Prettifier.prettify_pg_err(<<~ERR, raw_sql )
        ERROR:  VALUES in FROM must have an alias
        LINE 2:  FROM ( VALUES(1), (2) )
        HINT:  For example, FROM (VALUES ...) [AS] foo.

    # 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

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.


Right now gem detects only uppercased form of verbs with simple indentation and parsing options.


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.