build_subselect

# File activerecord/lib/arel/visitors/to_sql.rb, line 815
        def build_subselect(key, o)
          stmt             = Nodes::SelectStatement.new
          core             = stmt.cores.first
          core.froms       = o.relation
          core.wheres      = o.wheres
          core.projections = [key]
          stmt.limit       = o.limit
          stmt.offset      = o.offset
          stmt.orders      = o.orders
          stmt
        end