Method reset

sql/field.h:4217–4221

  bool zero_pack() const override { return false; }
  Copy_func *get_copy_func(const Field *from) const override;
  int reset() override
  {
    charset()->fill((char*) ptr, field_length, (has_charset() ? ' ' : 0));
    return 0;
  }
  int store(const char *to,size_t length,CHARSET_INFO *charset) override;
  using Field_str::store;
  double val_real() override;