Where clause with join, group and sum generates ERROR in Rails 4.1.8

[roscom]

Config: rails 4.1.8 squeel-1.2.2 The following squeel code works:

# == Schema Information
# 
# Table name: bank_accounts
# 
#  id              :integer          not null, primary key
# number          :string(255)
#  currency_id     :integer
#  created_at      :datetime
#  updated_at      :datetime
#  opening_balance :decimal(10, 2)
#  opening_date    :date

class BankAccount < ActiveRecord::Base
 has_many :accounts
 scope :trial_balance, -> {
   BankAccount.
       joins{accounts.transactions}.
       group{[number, opening_date]}.
       sum(:amount)
 }
end

However, when a where clause is applied to limit the resul set it fails

scope :trial_balance, -> {
   BankAccount.
       where{transactions.date.gt_eq bank_accounts.opening_date}.
       joins{accounts.transactions}.
       group{[number, opening_date]}.
       sum(:amount)
 }

with the following error: neither group nor sum are recognised:

irb(main):055:0> BankAccount.trial_balance
NoMethodError:   BankAccount Load (0.1ms)  SELECT `bank_accounts`.* FROM `bank_accounts` INNER JOIN `accounts` ON `accounts`.`bank_account_id` = `bank_accounts`.`id` INNER JOIN `transactions` ON `transactions`.`account_id` = `accounts`.`id`
undefined method `group' for #<ActiveRecord::QueryMethods::WhereChain:0x007f610e427310>
        from /home/christopher/work/trust-accounts/app/models/bank_account.rb:23:in `block in <class:BankAccount>'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/scoping/named.rb:151:in `call'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/scoping/named.rb:151:in `block (2 levels) in scope'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/relation.rb:292:in `scoping'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/scoping/named.rb:151:in `block in scope'
        from (irb):55
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:90:in `start'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/console.rb:9:in `start'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:69:in `console'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
        from /home/christopher/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.1.8/lib/rails/commands.rb:17:in `<top (required)>'
        from bin/rails:4:in `require'
        from bin/rails:4:in `<main>'

The SQL it should generate is perfectly legal, as in

select number, opening_date, sum(t.amount) 
from bank_accounts b, accounts a, transactions t
where b.id = a.bank_account_id and a.id = t.account_id  and t.date >= b.opening_date
group by number, opening_date

Would appreciate very much if you could take a look & point out any errors in my syntax or suggest how this query may otherwise be written using squeel

Regards