ClickHouse/docs/en/sql-reference/functions/window-view-functions.md

---
toc_priority: 68
toc_title: Window View
---

# Window View Functions {#window-view-functions}

Window functions indicate the lower and upper window bound of records in WindowView. The functions for working with WindowView are listed below.

## tumble {#window-view-functions-tumble}

A tumbling time window assigns records to non-overlapping, continuous windows with a fixed duration (interval). 

``` sql
tumble(time_attr, interval [, timezone])
```

**Arguments**
- `time_attr` - Date and time. [DateTime](../../sql-reference/data-types/datetime.md) data type.
- `interval` - Window interval in [Interval](../../sql-reference/data-types/special-data-types/interval.md) data type.
- `timezone` — [Timezone name](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-timezone) (optional). 

**Returned values**

-  The lower and upper bound of the tumble window.

Type: `Tuple(DateTime, DateTime)`

**Example**

Query:

``` sql
SELECT tumble(now(), toIntervalDay('1'))
```

Result:

``` text
┌─tumble(now(), toIntervalDay('1'))─────────────┐
│ ['2020-01-01 00:00:00','2020-01-02 00:00:00'] │
└───────────────────────────────────────────────┘
```

## hop {#window-view-functions-hop}

A hopping time window has a fixed duration (`window_interval`) and hops by a specified hop interval (`hop_interval`). If the `hop_interval` is smaller than the `window_interval`, hopping windows are overlapping. Thus, records can be assigned to multiple windows. 

``` sql
hop(time_attr, hop_interval, window_interval [, timezone])
```

**Arguments**

- `time_attr` - Date and time. [DateTime](../../sql-reference/data-types/datetime.md) data type.
- `hop_interval` - Hop interval in [Interval](../../sql-reference/data-types/special-data-types/interval.md) data type. Should be a positive number.
- `window_interval` - Window interval in [Interval](../../sql-reference/data-types/special-data-types/interval.md) data type. Should be a positive number.
- `timezone` — [Timezone name](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-timezone) (optional). 

**Returned values**

-  The lower and upper bound of the hop window. Since hop windows are
   overlapped, the function only returns the bound of the **first** window when
   hop function is used **without** `WINDOW VIEW`.

Type: `Tuple(DateTime, DateTime)`

**Example**

Query:

``` sql
SELECT hop(now(), INTERVAL '1' SECOND, INTERVAL '2' SECOND)
```

Result:

``` text
┌─hop(now(), toIntervalSecond('1'), toIntervalSecond('2'))──┐
│ ('2020-01-14 16:58:22','2020-01-14 16:58:24')             │
└───────────────────────────────────────────────────────────┘
```

## tumbleStart {#window-view-functions-tumblestart}

Indicate the lower bound of a tumble function.

``` sql
tumbleStart(time_attr, interval [, timezone]);
```

## tumbleEnd {#window-view-functions-tumbleend}

Indicate the upper bound of a tumble function.

``` sql
tumbleEnd(time_attr, interval [, timezone]);
```

## hopStart {#window-view-functions-hopstart}

Indicate the lower bound of a hop function.

``` sql
hopStart(time_attr, hop_interval, window_interval [, timezone]);
```

## hopEnd {#window-view-functions-hopend}

Indicate the upper bound of a hop function.

``` sql
hopEnd(time_attr, hop_interval, window_interval [, timezone]);
```