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25 lines
720 B
Markdown
25 lines
720 B
Markdown
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<a name="special_data_type-nothing"></a>
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# Nothing
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此数据类型的唯一目的是表示不是期望值的情况。 所以你不能创建一个` Nothing` 类型的值。
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例如， [NULL](../../query_language/syntax.md#null-literal) 有 `Nullable(Nothing)`。更多参见[Nullable](../../data_types/nullable.md#data_type-nullable).
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`Nothing` 类型也可用于表示空数组：
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```bash
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:) SELECT toTypeName(array())
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SELECT toTypeName([])
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┌─toTypeName(array())─┐
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│ Array(Nothing) │
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└─────────────────────┘
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1 rows in set. Elapsed: 0.062 sec.
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```
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[来源文章](https://clickhouse.yandex/docs/en/data_types/special_data_types/nothing/) <!--hide-->
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