  Key_part_spec(const char *name, const size_t name_len, uint len)
    : length(len)
  { field_name.str= (char *)name; field_name.length= name_len; }
  Key_part_spec(const char *name, const size_t name_len, uint len)
    : length(len)
  { field_name.str= (char *)name; field_name.length= name_len; }