code: func builtinReplace(args []types.Datum, _ context.Context) (d types.Datum, err error) {
  	for _, arg := range args {
  		if arg.IsNull() {
  			return d, nil
  		}
  	}
  
  	str, err := args[0].ToString()
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	oldStr, err := args[1].ToString()
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	newStr, err := args[2].ToString()
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	d.SetString(strings.Replace(str, oldStr, newStr, -1))
  
  	return d, nil
  }
docs: // See https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_replace