module Sequel::IBMDB::Dataset::CallableStatementMethods

def subselect_sql_append(sql, ds)

prepared statements work.
Extend given dataset with this module so subselects inside subselects in 
def subselect_sql_append(sql, ds)
  ps = ds.to_prepared_statement(:select).clone(:append_sql=>sql)
  ps.extend(CallableStatementMethods)
  ps = ps.bind(@opts[:bind_vars]) if @opts[:bind_vars]
  ps.prepared_args = prepared_args
  ps.prepared_sql
end