code: func (b *builtinCRC32Sig) evalInt(row chunk.Row) (int64, bool, error) {
  	x, isNull, err := b.args[0].EvalString(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  	r := crc32.ChecksumIEEE([]byte(x))
  	return int64(r), false, nil
  }
docs: // evalInt evals a CRC32(expr).
  // See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_crc32