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61 lines
2.6 KiB
Markdown
61 lines
2.6 KiB
Markdown
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# UUID {#uuid-data-type}
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Universally unique identifier (UUID) is a 16-byte number used to identify the records. For detailed information about the UUID, see [Wikipedia](https://en.wikipedia.org/wiki/Universally_unique_identifier).
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The example of UUID type value is represented below:
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```
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61f0c404-5cb3-11e7-907b-a6006ad3dba0
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```
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If you do not specify the UUID column value when inserting a new record, the UUID value is filled with zero:
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```
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00000000-0000-0000-0000-000000000000
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```
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## How to generate
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To generate the UUID value, ClickHouse provides the [generateUUIDv4](../query_language/functions/uuid_functions.md) function.
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## Usage example
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**Example 1**
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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, y String) ENGINE=TinyLog
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:) INSERT INTO t_uuid SELECT generateUUIDv4(), 'Example 1'
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:) SELECT * FROM t_uuid
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┌────────────────────────────────────x─┬─y─────────┐
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│ 417ddc5d-e556-4d27-95dd-a34d84e46a50 │ Example 1 │
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└──────────────────────────────────────┴───────────┘
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```
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**Example 2**
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In this example, the UUID column value is not specified when inserting a new record.
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``` sql
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:) INSERT INTO t_uuid (y) VALUES ('Example 2')
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:) SELECT * FROM t_uuid
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┌────────────────────────────────────x─┬─y─────────┐
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│ 417ddc5d-e556-4d27-95dd-a34d84e46a50 │ Example 1 │
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│ 00000000-0000-0000-0000-000000000000 │ Example 2 │
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└──────────────────────────────────────┴───────────┘
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```
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## Restrictions
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The UUID data type only supports functions which [String](string.md) data type also supports (for example, [min](../query_language/agg_functions/reference.md#agg_function-min), [max](../query_language/agg_functions/reference.md#agg_function-max), and [count](../query_language/agg_functions/reference.md#agg_function-count)).
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The UUID data type is not supported by arithmetic operations (for example, [abs](../query_language/functions/arithmetic_functions.md#arithm_func-abs)) neither aggregate functions, such as [sum](../query_language/agg_functions/reference.md#agg_function-sum) and [avg](../query_language/agg_functions/reference.md#agg_function-avg).
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[Original article](https://clickhouse.yandex/docs/en/data_types/uuid/) <!--hide-->
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