public String indexToName(int index) {
        try {
            return columns.get(index).getColumnName();
        } catch (IndexOutOfBoundsException e) {
            throw new NoSuchColumnException("Result has no column with index = " + index);
        }
    }
Takes absolute index (starting from 0) and returns corresponding column.

@param index - column index starting from 0
@return - column name
client-v2/src/main/java/com/clickhouse/client/api/metadata/TableSchema.java