presto-cassandra/src/main/java/io/prestosql/plugin/cassandra/util/CassandraCqlUtils.java/CassandraCqlUtils/appendSelectColumns
class CassandraCqlUtils:    private static void appendSelectColumns(StringBuilder stringBuilder, List<? extends ColumnHandle> columns, boolean first)
    {
        for (ColumnHandle column : columns) {
            if (first) {
                first = false;
            }
            else {
                stringBuilder.append(",");
            }
            stringBuilder.append(validColumnName(((CassandraColumnHandle) column).getName()));
        }
    }