  Rewritable_query_parameter(uint pos_in_q= 0, uint len_in_q= 0)
    : pos_in_query(pos_in_q), len_in_query(len_in_q),
      limit_clause_param(false)
  { }
  Rewritable_query_parameter(uint pos_in_q= 0, uint len_in_q= 0)
    : pos_in_query(pos_in_q), len_in_query(len_in_q),
      limit_clause_param(false)
  { }