error.rb

2.1.5 :001 > require './app'
 => true 
2.1.5 :002 > @cal = DreamColorMonitor.select('dream_color_monitors.id, c.dream_color_monitor_id, tag, min(date)').joins('JOIN calibrations c ON dream_color_monitors.id = c.dream_color_monitor_id').where("date > date('now') - 90").group('tag')
ActiveRecord::StatementInvalid: PG::GroupingError: ERROR:  column "dream_color_monitors.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT dream_color_monitors.id, c.dream_color_monitor_id, ta...
               ^
: SELECT dream_color_monitors.id, c.dream_color_monitor_id, tag, min(date) FROM "dream_color_monitors" JOIN calibrations c ON dream_color_monitors.id = c.dream_color_monitor_id WHERE (date > date('now') - 90) GROUP BY "dream_color_monitors"."tag"
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:592:in `async_exec'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:592:in `block in exec_no_cache'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_adapter.rb:473:in `block in log'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activesupport-4.2.1/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_adapter.rb:467:in `log'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:592:in `exec_no_cache'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/postgresql_adapter.rb:584:in `execute_and_clear'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/postgresql/database_statements.rb:160:in `exec_query'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:347:in `select'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:32:in `select_all'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/query_cache.rb:70:in `select_all'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/querying.rb:39:in `find_by_sql'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/relation.rb:638:in `exec_queries'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/relation.rb:514:in `load'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/relation.rb:243:in `to_a'
        from /usr/local/rvm/gems/ruby-2.1.5/gems/activerecord-4.2.1/lib/active_record/relation.rb:629:in `inspect'
        from /usr/local/rvm/rubies/ruby-2.1.5/bin/irb:11:in `<main>'2.1.5 :003 >