code: func (s *SessionVars) GetCharsetInfo() (charset, collation string) {
  	charset = s.systems[CharacterSetConnection]
  	collation = s.systems[CollationConnection]
  	return
  }
docs: // GetCharsetInfo gets charset and collation for current context.
  // What character set should the server translate a statement to after receiving it?
  // For this, the server uses the character_set_connection and collation_connection system variables.
  // It converts statements sent by the client from character_set_client to character_set_connection
  // (except for string literals that have an introducer such as _latin1 or _utf8).
  // collation_connection is important for comparisons of literal strings.
  // For comparisons of strings with column values, collation_connection does not matter because columns
  // have their own collation, which has a higher collation precedence.
  // See https://dev.mysql.com/doc/refman/5.7/en/charset-connection.html