Functions for Working with UUIDs

generateUUIDv4

Generates a version 4 UUID.

Syntax

Arguments

• expr — An arbitrary expression used to bypass common subexpression elimination if the function is called multiple times in a query. The value of the expression has no effect on the returned UUID. Optional.

Returned value

A value of type UUIDv4.

Example

First, create a table with a column of type UUID, then insert a generated UUIDv4 into the table.

Result:

Example with multiple UUIDs generated per row

generateUUIDv7

Generates a version 7 UUID.

The generated UUID contains the current Unix timestamp in milliseconds (48 bits), followed by version "7" (4 bits), a counter (42 bit) to distinguish UUIDs within a millisecond (including a variant field "2", 2 bit), and a random field (32 bits). For any given timestamp (unix_ts_ms), the counter starts at a random value and is incremented by 1 for each new UUID until the timestamp changes. In case the counter overflows, the timestamp field is incremented by 1 and the counter is reset to a random new start value.

Function generateUUIDv7 guarantees that the counter field within a timestamp increments monotonically across all function invocations in concurrently running threads and queries.

Note

As of April 2024, version 7 UUIDs are in draft status and their layout may change in future.

Syntax

Arguments

• expr — An arbitrary expression used to bypass common subexpression elimination if the function is called multiple times in a query. The value of the expression has no effect on the returned UUID. Optional.

Returned value

A value of type UUIDv7.

Example

First, create a table with a column of type UUID, then insert a generated UUIDv7 into the table.

Result:

Example with multiple UUIDs generated per row

empty

Checks whether the input UUID is empty.

Syntax

The UUID is considered empty if it contains all zeros (zero UUID).

The function also works for Arrays and Strings.

Arguments

• x — A UUID. UUID.

Returned value

• Returns 1 for an empty UUID or 0 for a non-empty UUID. UInt8.

Example

To generate the UUID value, ClickHouse provides the generateUUIDv4 function.

Query:

Result:

notEmpty

Checks whether the input UUID is non-empty.

Syntax

The UUID is considered empty if it contains all zeros (zero UUID).

The function also works for Arrays or Strings.

Arguments

• x — A UUID. UUID.

Returned value

• Returns 1 for a non-empty UUID or 0 for an empty UUID. UInt8.

Example

To generate the UUID value, ClickHouse provides the generateUUIDv4 function.

Query:

Result:

toUUID

Converts a value of type String to a UUID.

Returned value

The UUID type value.

Usage example

Result:

toUUIDOrDefault

Arguments

• string — String of 36 characters or FixedString(36). String.
• default — UUID to be used as the default if the first argument cannot be converted to a UUID type. UUID.

Returned value

UUID

Returned value

The UUID type value.

Usage examples

This first example returns the first argument converted to a UUID type as it can be converted:

Result:

This second example returns the second argument (the provided default UUID) as the first argument cannot be converted to a UUID type:

Result:

toUUIDOrNull

Takes an argument of type String and tries to parse it into UUID. If failed, returns NULL.

Returned value

The Nullable(UUID) type value.

Usage example

Result:

toUUIDOrZero

It takes an argument of type String and tries to parse it into UUID. If failed, returns zero UUID.

Returned value

The UUID type value.

Usage example

Result:

UUIDStringToNum

Accepts string containing 36 characters in the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, and returns a FixedString(16) as its binary representation, with its format optionally specified by variant (Big-endian by default).

Syntax

Arguments

• string — A String of 36 characters or FixedString
• variant — Integer, representing a variant as specified by RFC4122. 1 = Big-endian (default), 2 = Microsoft.

Returned value

FixedString(16)

Usage examples

Result:

Result:

UUIDNumToString

Accepts binary containing a binary representation of a UUID, with its format optionally specified by variant (Big-endian by default), and returns a string containing 36 characters in text format.

Syntax

Arguments

• binary — FixedString(16) as a binary representation of a UUID.
• variant — Integer, representing a variant as specified by RFC4122. 1 = Big-endian (default), 2 = Microsoft.

Returned value

String.

Usage example

Result:

Result:

UUIDToNum

Accepts a UUID and returns its binary representation as a FixedString(16), with its format optionally specified by variant (Big-endian by default). This function replaces calls to two separate functions UUIDStringToNum(toString(uuid)) so no intermediate conversion from UUID to string is required to extract bytes from a UUID.

Syntax

Arguments

• uuid — UUID.
• variant — Integer, representing a variant as specified by RFC4122. 1 = Big-endian (default), 2 = Microsoft.

Returned value

The binary representation of the UUID.

Usage examples

Result:

Result:

UUIDv7ToDateTime

Returns the timestamp component of a UUID version 7.

Syntax

Arguments

• uuid — UUID of version 7.
• timezone — Timezone name for the returned value (optional). String.

Returned value

• Timestamp with milliseconds precision. If the UUID is not a valid version 7 UUID, it returns 1970-01-01 00:00:00.000. DateTime64(3).

Usage examples

Result:

Result:

serverUUID

Returns the random UUID generated during the first start of the ClickHouse server. The UUID is stored in file uuid in the ClickHouse server directory (e.g. /var/lib/clickhouse/) and retained between server restarts.

Syntax

Returned value

• The UUID of the server. UUID.

generateSnowflakeID

Generates a Snowflake ID.

The generated Snowflake ID contains the current Unix timestamp in milliseconds (41 + 1 top zero bits), followed by a machine id (10 bits), and a counter (12 bits) to distinguish IDs within a millisecond. For any given timestamp (unix_ts_ms), the counter starts at 0 and is incremented by 1 for each new Snowflake ID until the timestamp changes. In case the counter overflows, the timestamp field is incremented by 1 and the counter is reset to 0.

Function generateSnowflakeID guarantees that the counter field within a timestamp increments monotonically across all function invocations in concurrently running threads and queries.

Note

The generated Snowflake IDs are based on the UNIX epoch 1970-01-01. While no standard or recommendation exists for the epoch of Snowflake IDs, implementations in other systems may use a different epoch, e.g. Twitter/X (2010-11-04) or Mastodon (2015-01-01).

Syntax

Arguments

• expr — An arbitrary expression used to bypass common subexpression elimination if the function is called multiple times in a query. The value of the expression has no effect on the returned Snowflake ID. Optional.
• machine_id — A machine ID, the lowest 10 bits are used. Int64. Optional.

Returned value

A value of type UInt64.

Example

First, create a table with a column of type UInt64, then insert a generated Snowflake ID into the table.

Result:

Example with multiple Snowflake IDs generated per row

Example with expression and a machine ID

snowflakeToDateTime

Deprecated feature

Danger

This function is deprecated and can only be used if setting allow_deprecated_snowflake_conversion_functions is enabled. The function will be removed at some point in future.

Extracts the timestamp component of a Snowflake ID in DateTime format.

Syntax

Arguments

• value — Snowflake ID. Int64.
• time_zone — Timezone. The function parses time_string according to the timezone. Optional. String.

Returned value

• The timestamp component of value as a DateTime value.

Example

Query:

Result:

snowflakeToDateTime64

Deprecated feature

Danger

This function is deprecated and can only be used if setting allow_deprecated_snowflake_conversion_functions is enabled. The function will be removed at some point in future.

Extracts the timestamp component of a Snowflake ID in DateTime64 format.

Syntax

Arguments

• value — Snowflake ID. Int64.
• time_zone — Timezone. The function parses time_string according to the timezone. Optional. String.

Returned value

• The timestamp component of value as a DateTime64 with scale = 3, i.e. millisecond precision.

Example

Query:

Result:

dateTimeToSnowflake

Deprecated feature

Danger

This function is deprecated and can only be used if setting allow_deprecated_snowflake_conversion_functions is enabled. The function will be removed at some point in future.

Converts a DateTime value to the first Snowflake ID at the giving time.

Syntax

Arguments

• value — Date with time. DateTime.

Returned value

• Input value converted to the Int64 data type as the first Snowflake ID at that time.

Example

Query:

Result:

dateTime64ToSnowflake

Deprecated feature

Danger

This function is deprecated and can only be used if setting allow_deprecated_snowflake_conversion_functions is enabled. The function will be removed at some point in future.

Convert a DateTime64 to the first Snowflake ID at the giving time.

Syntax

Arguments

• value — Date with time. DateTime64.

Returned value

• Input value converted to the Int64 data type as the first Snowflake ID at that time.

Example

Query:

Result:

snowflakeIDToDateTime

Returns the timestamp component of a Snowflake ID as a value of type DateTime.

Syntax

Arguments

• value — Snowflake ID. UInt64.
• epoch - Epoch of the Snowflake ID in milliseconds since 1970-01-01. Defaults to 0 (1970-01-01). For the Twitter/X epoch (2015-01-01), provide 1288834974657. Optional. UInt*.
• time_zone — Timezone. The function parses time_string according to the timezone. Optional. String.

Returned value

• The timestamp component of value as a DateTime value.

Example

Query:

Result:

snowflakeIDToDateTime64

Returns the timestamp component of a Snowflake ID as a value of type DateTime64.

Syntax

Arguments

• value — Snowflake ID. UInt64.
• epoch - Epoch of the Snowflake ID in milliseconds since 1970-01-01. Defaults to 0 (1970-01-01). For the Twitter/X epoch (2015-01-01), provide 1288834974657. Optional. UInt*.
• time_zone — Timezone. The function parses time_string according to the timezone. Optional. String.

Returned value

• The timestamp component of value as a DateTime64 with scale = 3, i.e. millisecond precision.

Example

Query:

Result:

dateTimeToSnowflakeID

Converts a DateTime value to the first Snowflake ID at the giving time.

Syntax

Arguments

• value — Date with time. DateTime.
• epoch - Epoch of the Snowflake ID in milliseconds since 1970-01-01. Defaults to 0 (1970-01-01). For the Twitter/X epoch (2015-01-01), provide 1288834974657. Optional. UInt*.

Returned value

• Input value converted to UInt64 as the first Snowflake ID at that time.

Example

Query:

Result:

dateTime64ToSnowflakeID

Convert a DateTime64 to the first Snowflake ID at the giving time.

Syntax

Arguments

• value — Date with time. DateTime64.
• epoch - Epoch of the Snowflake ID in milliseconds since 1970-01-01. Defaults to 0 (1970-01-01). For the Twitter/X epoch (2015-01-01), provide 1288834974657. Optional. UInt*.

Returned value

• Input value converted to UInt64 as the first Snowflake ID at that time.

Example

Query:

Result:

See also

• dictGetUUID