code: func (c *Column) String() string {
  	ans := []string{c.Name.O, types.TypeToStr(c.Tp, c.Charset)}
  	if mysql.HasAutoIncrementFlag(c.Flag) {
  		ans = append(ans, "AUTO_INCREMENT")
  	}
  	if mysql.HasNotNullFlag(c.Flag) {
  		ans = append(ans, "NOT NULL")
  	}
  	return strings.Join(ans, " ")
  }
docs: // String implements fmt.Stringer interface.