How to: $rateColumns(key, value) - is a combination of $columns and $rate
Example usage:

```sql
$rateColumns(OS, count(*) c) FROM requests
```

Query will be transformed into:

```sql
SELECT
    t,
    arrayMap(lambda(tuple(a), (a.1, a.2 / runningDifference(t / 1000))), groupArr)
FROM
(
    SELECT
        t,
        groupArray((OS, c)) AS groupArr
    FROM
    (
        SELECT
            (intDiv(toUInt32(EventTime), 60) * 60) * 1000 AS t,
            OS,
            count(*) AS c
        FROM requests
        WHERE ((EventDate >= toDate(1482796867)) AND (EventDate <= toDate(1482853383))) AND ((EventTime >= toDateTime(1482796867)) AND (EventTime <= toDateTime(1482853383)))
        GROUP BY
            t,
            OS
        ORDER BY
            t,
            OS
    )
    GROUP BY t
    ORDER BY t
)

```

---