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83 lines
2.4 KiB
Markdown
83 lines
2.4 KiB
Markdown
# Array(T) {#data_type-array}
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由 `T` 类型元素组成的数组。
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`T` 可以是任意类型，包含数组类型。 但不推荐使用多维数组，ClickHouse 对多维数组的支持有限。例如，不能存储在 `MergeTree` 表中存储多维数组。
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## 创建数组
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您可以使用array函数来创建数组：
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```
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array(T)
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```
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您也可以使用方括号：
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```
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[]
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```
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创建数组示例：
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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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## 使用数据类型
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ClickHouse会自动检测数组元素,并根据元素计算出存储这些元素最小的数据类型。如果在元素中存在 [NULL](../query_language/syntax.md#null-literal) 或存在 [Nullable](nullable.md#data_type-nullable) 类型元素，那么数组的元素类型将会变成 [Nullable](nullable.md)。
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如果 ClickHouse 无法确定数据类型，它将产生异常。当尝试同时创建一个包含字符串和数字的数组时会发生这种情况 (`SELECT array(1, 'a')`)。
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自动数据类型检测示例：
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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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如果您尝试创建不兼容的数据类型数组，ClickHouse 将引发异常：
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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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