other_functions.md

# Other functions

## hostName()

Returns a string with the name of the host that this function was performed on. For distributed processing, this is the name of the remote server host, if the function is performed on a remote server.

## visibleWidth(x)

Calculates the approximate width when outputting values to the console in text format (tab-separated).
This function is used by the system for implementing Pretty formats.

## toTypeName(x)

Returns a string containing the type name of the passed argument.

## blockSize()

Gets the size of the block.
In ClickHouse, queries are always run on blocks (sets of column parts). This function allows getting the size of the block that you called it for.

## materialize(x)

Turns a constant into a full column containing just one value.
In ClickHouse, full columns and constants are represented differently in memory. Functions work differently for constant arguments and normal arguments (different code is executed), although the result is almost always the same. This function is for debugging this behavior.

## ignore(...)

Accepts any arguments and always returns 0.
However, the argument is still evaluated. This can be used for benchmarks.

## sleep(seconds)

Sleeps 'seconds' seconds on each data block. You can specify an integer or a floating-point number.

## currentDatabase()

Returns the name of the current database.
You can use this function in table engine parameters in a CREATE TABLE query where you need to specify the database.

## isFinite(x)

Accepts Float32 and Float64 and returns UInt8 equal to 1 if the argument is not infinite and not a NaN, otherwise 0.

## isInfinite(x)

Accepts Float32 and Float64 and returns UInt8 equal to 1 if the argument is infinite, otherwise 0. Note that 0 is returned for a NaN.

## isNaN(x)

Accepts Float32 and Float64 and returns UInt8 equal to 1 if the argument is a NaN, otherwise 0.

## hasColumnInTable(\['hostname'\[, 'username'\[, 'password'\]\],\] 'database', 'table', 'column')

Accepts constant strings: database name, table name, and column name. Returns a UInt8 constant expression equal to 1 if there is a column, otherwise 0. If the hostname parameter is set, the test will run on a remote server.
The function throws an exception if the table does not exist.
For elements in a nested data structure, the function checks for the existence of a column. For the nested data structure itself, the function returns 0.

## bar

Allows building a unicode-art diagram.

`bar (x, min, max, width)` – Draws a band with a width proportional to (x - min) and equal to 'width' characters when x == max.`min, max` – Integer constants. The value must fit in Int64.`width` – Constant, positive number, may be a fraction.

The band is drawn with accuracy to one eighth of a symbol.

Example:

```sql
SELECT
    toHour(EventTime) AS h,
    count() AS c,
    bar(c, 0, 600000, 20) AS bar
FROM test.hits
GROUP BY h
ORDER BY h ASC
```

```text
┌──h─┬──────c─┬─bar────────────────┐
│  0 │ 292907 │ █████████▋         │
│  1 │ 180563 │ ██████             │
│  2 │ 114861 │ ███▋               │
│  3 │  85069 │ ██▋                │
│  4 │  68543 │ ██▎                │
│  5 │  78116 │ ██▌                │
│  6 │ 113474 │ ███▋               │
│  7 │ 170678 │ █████▋             │
│  8 │ 278380 │ █████████▎         │
│  9 │ 391053 │ █████████████      │
│ 10 │ 457681 │ ███████████████▎   │
│ 11 │ 493667 │ ████████████████▍  │
│ 12 │ 509641 │ ████████████████▊  │
│ 13 │ 522947 │ █████████████████▍ │
│ 14 │ 539954 │ █████████████████▊ │
│ 15 │ 528460 │ █████████████████▌ │
│ 16 │ 539201 │ █████████████████▊ │
│ 17 │ 523539 │ █████████████████▍ │
│ 18 │ 506467 │ ████████████████▊  │
│ 19 │ 520915 │ █████████████████▎ │
│ 20 │ 521665 │ █████████████████▍ │
│ 21 │ 542078 │ ██████████████████ │
│ 22 │ 493642 │ ████████████████▍  │
│ 23 │ 400397 │ █████████████▎     │
└────┴────────┴────────────────────┘
```

<a name="other_functions-transform"></a>

## transform

Transforms a value according to the explicitly defined mapping of some elements to other ones.
There are two variations of this function:

1. `transform(x, array_from, array_to, default)`

`x` – What to transform.

`array_from` – Constant array of values for converting.

`array_to` – Constant array of values to convert the values in 'from' to.

`default` – Which value to use if 'x' is not equal to any of the values in 'from'.

`array_from` and `array_to` – Arrays of the same size.

Types:

`transform(T, Array(T), Array(U), U) -> U`

`T` and `U` can be numeric, string, or Date or DateTime types.
Where the same letter is indicated (T or U), for numeric types these might not be matching types, but types that have a common type.
For example, the first argument can have the Int64 type, while the second has the Array(Uint16) type.

If the 'x' value is equal to one of the elements in the 'array_from' array, it returns the existing element (that is numbered the same) from the 'array_to' array. Otherwise, it returns 'default'. If there are multiple matching elements in 'array_from', it returns one of the matches.

Example:

```sql
SELECT
    transform(SearchEngineID, [2, 3], ['Yandex', 'Google'], 'Other' AS title,
    count() AS c
FROM test.hits
WHERE SearchEngineID != 0
GROUP BY title
ORDER BY c DESC
```

```text
┌─title─────┬──────c─┐
│ Yandex    │ 498635 │
│ Google    │ 229872 │
│ Other     │ 104472 │
└───────────┴────────┘
```

2. `transform(x, array_from, array_to)`

Differs from the first variation in that the 'default' argument is omitted.
If the 'x' value is equal to one of the elements in the 'array_from' array, it returns the matching element (that is numbered the same) from the 'array_to' array. Otherwise, it returns 'x'.

Types:

`transform(T, Array(T), Array(T)) -> T`

Example:

```sql
SELECT
    transform(domain(Referer), ['yandex.ru', 'google.ru', 'vk.com'], ['www.yandex', 'example.com']) AS s,
    count() AS c
FROM test.hits
GROUP BY domain(Referer)
ORDER BY count() DESC
LIMIT 10
```

```text
┌─s──────────────┬───────c─┐
│                │ 2906259 │
│ www.yandex     │  867767 │
│ ███████.ru     │  313599 │
│ mail.yandex.ru │  107147 │
│ ██████.ru      │  100355 │
│ █████████.ru   │   65040 │
│ news.yandex.ru │   64515 │
│ ██████.net     │   59141 │
│ example.com    │   57316 │
└────────────────┴─────────┘
```

## formatReadableSize(x)

Accepts the size (number of bytes). Returns a rounded size with a suffix (KiB, MiB, etc.) as a string.

Example:

```sql
SELECT
    arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
    formatReadableSize(filesize_bytes) AS filesize
```

```text
┌─filesize_bytes─┬─filesize───┐
│              1 │ 1.00 B     │
│           1024 │ 1.00 KiB   │
│        1048576 │ 1.00 MiB   │
│      192851925 │ 183.92 MiB │
└────────────────┴────────────┘
```

## least(a, b)

Returns the smallest value from a and b.

## greatest(a, b)

Returns the largest value of a and b.

## uptime()

Returns the server's uptime in seconds.

## version()

Returns the version of the server as a string.

## rowNumberInAllBlocks()

Returns the ordinal number of the row in the data block. This function only considers the affected data blocks.

## runningDifference(x)

Calculates the difference between successive row values ​​in the data block.
Returns 0 for the first row and the difference from the previous row for each subsequent row.

The result of the function depends on the affected data blocks and the order of data in the block.
If you make a subquery with ORDER BY and call the function from outside the subquery, you can get the expected result.

Example:

```sql
SELECT
    EventID,
    EventTime,
    runningDifference(EventTime) AS delta
FROM
(
    SELECT
        EventID,
        EventTime
    FROM events
    WHERE EventDate = '2016-11-24'
    ORDER BY EventTime ASC
    LIMIT 5
)
```

```text
┌─EventID─┬───────────EventTime─┬─delta─┐
│    1106 │ 2016-11-24 00:00:04 │     0 │
│    1107 │ 2016-11-24 00:00:05 │     1 │
│    1108 │ 2016-11-24 00:00:05 │     0 │
│    1109 │ 2016-11-24 00:00:09 │     4 │
│    1110 │ 2016-11-24 00:00:10 │     1 │
└─────────┴─────────────────────┴───────┘
```

## MACNumToString(num)

Accepts a UInt64 number. Interprets it as a MAC address in big endian. Returns a string containing the corresponding MAC address in the format AA:BB:CC:DD:EE:FF (colon-separated numbers in hexadecimal form).

## MACStringToNum(s)

The inverse function of MACNumToString. If the MAC address has an invalid format, it returns 0.

## MACStringToOUI(s)

Accepts a MAC address in the format AA:BB:CC:DD:EE:FF (colon-separated numbers in hexadecimal form). Returns the first three octets as a UInt64 number. If the MAC address has an invalid format, it returns 0.