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86 lines
2.5 KiB
Markdown
86 lines
2.5 KiB
Markdown
# Array(T) {#data_type-array}
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Array of `T`-type items.
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`T` can be anything, including an array. Use multi-dimensional arrays with caution. ClickHouse has limited support for multi-dimensional arrays. For example, they can't be stored in `MergeTree` tables.
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## Creating an array
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You can use a function to create an array:
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```
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array(T)
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```
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You can also use square brackets.
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```
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[]
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```
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Example of creating an array:
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```
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:) SELECT array(1, 2) AS x, toTypeName(x)
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SELECT
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[1, 2] AS x,
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toTypeName(x)
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┌─x─────┬─toTypeName(array(1, 2))─┐
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│ [1,2] │ Array(UInt8) │
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└───────┴─────────────────────────┘
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1 rows in set. Elapsed: 0.002 sec.
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:) SELECT [1, 2] AS x, toTypeName(x)
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SELECT
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[1, 2] AS x,
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toTypeName(x)
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┌─x─────┬─toTypeName([1, 2])─┐
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│ [1,2] │ Array(UInt8) │
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└───────┴────────────────────┘
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1 rows in set. Elapsed: 0.002 sec.
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```
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## Working with data types
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When creating an array on the fly, ClickHouse automatically defines the argument type as the narrowest data type that can store all the listed arguments. If there are any [NULL](../query_language/syntax.md#null-literal) or [Nullable](nullable.md#data_type-nullable) type arguments, the type of array elements is [Nullable](nullable.md).
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If ClickHouse couldn't determine the data type, it will generate an exception. For instance, this will happen when trying to create an array with strings and numbers simultaneously (`SELECT array(1, 'a')`).
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Examples of automatic data type detection:
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```
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:) SELECT array(1, 2, NULL) AS x, toTypeName(x)
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SELECT
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[1, 2, NULL] AS x,
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toTypeName(x)
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┌─x──────────┬─toTypeName(array(1, 2, NULL))─┐
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│ [1,2,NULL] │ Array(Nullable(UInt8)) │
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└────────────┴───────────────────────────────┘
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1 rows in set. Elapsed: 0.002 sec.
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```
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If you try to create an array of incompatible data types, ClickHouse throws an exception:
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```
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:) SELECT array(1, 'a')
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SELECT [1, 'a']
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Received exception from server (version 1.1.54388):
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Code: 386. DB::Exception: Received from localhost:9000, 127.0.0.1. DB::Exception: There is no supertype for types UInt8, String because some of them are String/FixedString and some of them are not.
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0 rows in set. Elapsed: 0.246 sec.
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```
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[Original article](https://clickhouse.yandex/docs/en/data_types/array/) <!--hide-->
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