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70 lines
2.0 KiB
Markdown
70 lines
2.0 KiB
Markdown
---
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slug: /zh/sql-reference/dictionaries/external-dictionaries/external-dicts-dict-hierarchical
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machine_translated: true
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machine_translated_rev: 72537a2d527c63c07aa5d2361a8829f3895cf2bd
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sidebar_position: 45
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sidebar_label: "\u5206\u5C42\u5B57\u5178"
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---
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# 分层字典 {#hierarchical-dictionaries}
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ClickHouse支持分层字典与 [数字键](external-dicts-dict-structure.md#ext_dict-numeric-key).
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看看下面的层次结构:
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``` text
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0 (Common parent)
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│
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├── 1 (Russia)
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│ │
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│ └── 2 (Moscow)
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│ │
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│ └── 3 (Center)
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│
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└── 4 (Great Britain)
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│
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└── 5 (London)
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```
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这种层次结构可以表示为下面的字典表。
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| region_id | parent_region | region_name |
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|------------|----------------|--------------|
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| 1 | 0 | 俄罗斯 |
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| 2 | 1 | 莫斯科 |
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| 3 | 2 | 中心 |
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| 4 | 0 | 英国 |
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| 5 | 4 | 伦敦 |
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此表包含一列 `parent_region` 包含该元素的最近父项的键。
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ClickHouse支持 [等级](external-dicts-dict-structure.md#hierarchical-dict-attr) 属性为 [外部字典](./external-dicts-dict-structure.md) 属性。 此属性允许您配置类似于上述的分层字典。
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该 [独裁主义](../../../sql-reference/functions/ext-dict-functions.md#dictgethierarchy) 函数允许您获取元素的父链。
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对于我们的例子，dictionary的结构可以是以下内容:
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``` xml
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<dictionary>
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<structure>
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<id>
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<name>region_id</name>
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</id>
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<attribute>
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<name>parent_region</name>
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<type>UInt64</type>
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<null_value>0</null_value>
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<hierarchical>true</hierarchical>
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</attribute>
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<attribute>
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<name>region_name</name>
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<type>String</type>
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<null_value></null_value>
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</attribute>
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</structure>
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</dictionary>
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```
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