code: func DefaultCharsetForType(tp byte) (string, string) {
  	switch tp {
  	case mysql.TypeVarString, mysql.TypeString, mysql.TypeVarchar:
  		// Default charset for string types is utf8.
  		return mysql.DefaultCharset, mysql.DefaultCollationName
  	}
  	return charset.CharsetBin, charset.CollationBin
  }
docs: // DefaultCharsetForType returns the default charset/collation for mysql type.