presto-jdbc/src/main/java/io/prestosql/jdbc/PrestoConnection.java/PrestoConnection/getIsolationLevel
class PrestoConnection:    private static String getIsolationLevel(int level)
            throws SQLException
    {
        switch (level) {
            case TRANSACTION_READ_UNCOMMITTED:
                return "READ UNCOMMITTED";
            case TRANSACTION_READ_COMMITTED:
                return "READ COMMITTED";
            case TRANSACTION_REPEATABLE_READ:
                return "REPEATABLE READ";
            case TRANSACTION_SERIALIZABLE:
                return "SERIALIZABLE";
        }
        throw new SQLException("Invalid transaction isolation level: " + level);
    }