Sequel::DatabaseError: TinyTds::Error: Incorrect syntax near the keyword 'AS'. from /home/echo/.rvm/gems/ruby-2.0.0-p0/gems/sequel-3.47.0/lib/sequel/adapters/tinytds.rb:234:in `fields'

actual.sql

SELECT ([SUBJECTID], [NUM_BDI_TIMEPOINTS])
FROM [SUBJECTIDENTIFIERS]
INNER JOIN (SELECT [SUBJECTID], count([BDI_TP]) AS [NUM_BDI_TIMEPOINTS]
            FROM [BDIS_OUTPUT]
            WHERE ((([BDI_TP] COLLATE Latin1_General_CS_AS)
                   LIKE
                   (N'Y%' COLLATE Latin1_General_CS_AS) ESCAPE N'\\'))
            GROUP BY [SUBJECTID]) AS [T1]
ON ([T1].[SUBJECTID] = [SUBJECTIDENTIFIERS].[SUBJECTID])

expected.sql

SELECT ([SUBJECTIDENTIFIERS].[SUBJECTID], [NUM_BDI_TIMEPOINTS])
FROM [SUBJECTIDENTIFIERS]
INNER JOIN (SELECT [SUBJECTID], count([BDI_TP]) AS [NUM_BDI_TIMEPOINTS]
            FROM [BDIS_OUTPUT]
            WHERE ([BDI_TP] LIKE 'Y%')
            GROUP BY [SUBJECTID]) AS [T1]
ON ([T1].[SUBJECTID] = [SUBJECTIDENTIFIERS].[SUBJECTID])

subject.rb

require 'sequel'

Sequel::Model.db = Sequel.tinytds(host:     "secretstuff",
                                  database: "secretstuff",
                                  username: "secretstuff",
                                  password: "secretstuff")

class Subject < Sequel::Model(:subjectidentifiers)
  set_primary_key :subjectid
  one_to_many :bdimeasures, :key => :subjectid

  def self.candidates()
    bdi_counts = BDIMeasure.
      select{[:subjectid, count(:bdi_tp).as(:num_bdi_timepoints)]}.
      grep(:bdi_tp, 'Y%').
      group_by(:subjectid)

    subjects = Subject.
      select([:subjectid, :num_bdi_timepoints]).
      join(bdi_counts, :subjectid => :subjectid).
      filter { num_bdi_timepoints >= 3 }
  end
end

class BDIMeasure < Sequel::Model(:bdis_output)
  set_primary_key [:subjectid, :bdi_tp]
  many_to_one :subject, :key => :subjectid
end