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267 lines
6.2 KiB
Markdown
267 lines
6.2 KiB
Markdown
---
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toc_priority: 53
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toc_title: UUID
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---
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# Functions for Working with UUID {#functions-for-working-with-uuid}
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The functions for working with UUID are listed below.
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## generateUUIDv4 {#uuid-function-generate}
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Generates the [UUID](../data-types/uuid.md) of [version 4](https://tools.ietf.org/html/rfc4122#section-4.4).
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``` sql
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generateUUIDv4()
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```
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**Returned value**
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The UUID type value.
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**Usage example**
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This example demonstrates creating a table with the UUID type column and inserting a value into the table.
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``` sql
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CREATE TABLE t_uuid (x UUID) ENGINE=TinyLog
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INSERT INTO t_uuid SELECT generateUUIDv4()
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SELECT * FROM t_uuid
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```
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``` text
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┌────────────────────────────────────x─┐
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│ f4bf890f-f9dc-4332-ad5c-0c18e73f28e9 │
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└──────────────────────────────────────┘
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```
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## empty {#empty}
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Checks whether the input UUID is empty.
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**Syntax**
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```sql
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empty(UUID)
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```
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The UUID is considered empty if it contains all zeros (zero UUID).
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The function also works for [arrays](array-functions.md#function-empty) or [strings](string-functions.md#empty).
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**Arguments**
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- `x` — Input UUID. [UUID](../data-types/uuid.md).
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**Returned value**
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- Returns `1` for an empty UUID or `0` for a non-empty UUID.
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Type: [UInt8](../data-types/int-uint.md).
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**Example**
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To generate the UUID value, ClickHouse provides the [generateUUIDv4](#uuid-function-generate) function.
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Query:
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```sql
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SELECT empty(generateUUIDv4());
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```
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Result:
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```text
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┌─empty(generateUUIDv4())─┐
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│ 0 │
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└─────────────────────────┘
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```
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## notEmpty {#notempty}
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Checks whether the input UUID is non-empty.
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**Syntax**
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```sql
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notEmpty(UUID)
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```
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The UUID is considered empty if it contains all zeros (zero UUID).
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The function also works for [arrays](array-functions.md#function-notempty) or [strings](string-functions.md#notempty).
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**Arguments**
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- `x` — Input UUID. [UUID](../data-types/uuid.md).
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**Returned value**
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- Returns `1` for a non-empty UUID or `0` for an empty UUID.
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Type: [UInt8](../data-types/int-uint.md).
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**Example**
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To generate the UUID value, ClickHouse provides the [generateUUIDv4](#uuid-function-generate) function.
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Query:
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```sql
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SELECT notEmpty(generateUUIDv4());
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```
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Result:
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```text
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┌─notEmpty(generateUUIDv4())─┐
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│ 1 │
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└────────────────────────────┘
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```
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## toUUID (x) {#touuid-x}
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Converts String type value to UUID type.
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``` sql
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toUUID(String)
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```
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**Returned value**
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The UUID type value.
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**Usage example**
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``` sql
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SELECT toUUID('61f0c404-5cb3-11e7-907b-a6006ad3dba0') AS uuid
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```
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``` text
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┌─────────────────────────────────uuid─┐
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│ 61f0c404-5cb3-11e7-907b-a6006ad3dba0 │
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└──────────────────────────────────────┘
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```
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## toUUIDOrNull (x) {#touuidornull-x}
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It takes an argument of type String and tries to parse it into UUID. If failed, returns NULL.
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``` sql
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toUUIDOrNull(String)
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```
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**Returned value**
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The Nullable(UUID) type value.
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**Usage example**
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``` sql
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SELECT toUUIDOrNull('61f0c404-5cb3-11e7-907b-a6006ad3dba0T') AS uuid
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```
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``` text
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┌─uuid─┐
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│ ᴺᵁᴸᴸ │
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└──────┘
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```
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## toUUIDOrZero (x) {#touuidorzero-x}
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It takes an argument of type String and tries to parse it into UUID. If failed, returns zero UUID.
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``` sql
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toUUIDOrZero(String)
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```
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**Returned value**
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The UUID type value.
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**Usage example**
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``` sql
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SELECT toUUIDOrZero('61f0c404-5cb3-11e7-907b-a6006ad3dba0T') AS uuid
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```
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``` text
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┌─────────────────────────────────uuid─┐
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│ 00000000-0000-0000-0000-000000000000 │
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└──────────────────────────────────────┘
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```
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## UUIDStringToNum {#uuidstringtonum}
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Accepts a string containing 36 characters in the format `xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`, and returns it as a set of bytes in a [FixedString(16)](../../sql-reference/data-types/fixedstring.md).
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``` sql
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UUIDStringToNum(String)
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```
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**Returned value**
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FixedString(16)
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**Usage examples**
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``` sql
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SELECT
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'612f3c40-5d3b-217e-707b-6a546a3d7b29' AS uuid,
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UUIDStringToNum(uuid) AS bytes
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```
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``` text
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┌─uuid─────────────────────────────────┬─bytes────────────┐
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│ 612f3c40-5d3b-217e-707b-6a546a3d7b29 │ a/<@];!~p{jTj={) │
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└──────────────────────────────────────┴──────────────────┘
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```
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## UUIDNumToString {#uuidnumtostring}
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Accepts a [FixedString(16)](../../sql-reference/data-types/fixedstring.md) value, and returns a string containing 36 characters in text format.
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``` sql
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UUIDNumToString(FixedString(16))
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```
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**Returned value**
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String.
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**Usage example**
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``` sql
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SELECT
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'a/<@];!~p{jTj={)' AS bytes,
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UUIDNumToString(toFixedString(bytes, 16)) AS uuid
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```
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``` text
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┌─bytes────────────┬─uuid─────────────────────────────────┐
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│ a/<@];!~p{jTj={) │ 612f3c40-5d3b-217e-707b-6a546a3d7b29 │
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└──────────────────┴──────────────────────────────────────┘
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```
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## serverUUID() {#server-uuid}
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Returns the random and unique UUID, which is generated when the server is first started and stored forever. The result writes to the file `uuid` created in the ClickHouse server directory `/var/lib/clickhouse/`.
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**Syntax**
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```sql
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serverUUID()
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```
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**Returned value**
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- The UUID of the server.
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Type: [UUID](../data-types/uuid.md).
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## See Also {#see-also}
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- [dictGetUUID](../../sql-reference/functions/ext-dict-functions.md#ext_dict_functions-other)
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