pg does not allow aliases in the having clause, but functions are fine

[arunagw]

Fixed tests.

master commit 5a05207

test_should_group_by_summed_field_having_condition_from_select(CalculationsTest):
ActiveRecord::StatementInvalid: PGError: ERROR:  column "min_credit_limit" does not exist
LINE 1: ... firm_id FROM "accounts"  GROUP BY firm_id HAVING min_credit...
                                                             ^
: SELECT SUM("accounts"."credit_limit") AS sum_credit_limit, MIN(credit_limit) AS min_credit_limit, firm_id AS firm_id FROM "accounts"  GROUP BY firm_id HAVING min_credit_limit > 50
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:962:in `async_exec'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:962:in `exec_no_cache'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:551:in `block in exec_query'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb:244:in `block in log'
    /Users/arunagw/checkouts/rails/activesupport/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb:239:in `log'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:550:in `exec_query'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:1031:in `select'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:18:in `select_all'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/relation/calculations.rb:258:in `execute_grouped_calculation'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/relation/calculations.rb:185:in `perform_calculation'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/relation/calculations.rb:155:in `calculate'
    /Users/arunagw/checkouts/rails/activerecord/lib/active_record/relation/calculations.rb:93:in `sum'
    /Users/arunagw/checkouts/rails/activerecord/test/cases/calculations_test.rb:174:in `test_should_group_by_summed_field_having_condition_from_select'
    /Users/arunagw/checkouts/rails/bundle/ruby/1.9.1/gems/mocha-0.9.12/lib/mocha/integration/mini_test/version_142_to_172.rb:27:in `run'
    /Users/arunagw/checkouts/rails/activesupport/lib/active_support/testing/setup_and_teardown.rb:35:in `block in run'
    /Users/arunagw/checkouts/rails/activesupport/lib/active_support/callbacks.rb:408:in `_run_setup_callbacks'