mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-04 21:42:39 +00:00
68 lines
2.1 KiB
Markdown
68 lines
2.1 KiB
Markdown
---
|
|
toc_priority: 45
|
|
toc_title: Hierarchical dictionaries
|
|
---
|
|
|
|
# Hierarchical Dictionaries {#hierarchical-dictionaries}
|
|
|
|
ClickHouse supports hierarchical dictionaries with a [numeric key](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict-numeric-key).
|
|
|
|
Look at the following hierarchical structure:
|
|
|
|
``` text
|
|
0 (Common parent)
|
|
│
|
|
├── 1 (Russia)
|
|
│ │
|
|
│ └── 2 (Moscow)
|
|
│ │
|
|
│ └── 3 (Center)
|
|
│
|
|
└── 4 (Great Britain)
|
|
│
|
|
└── 5 (London)
|
|
```
|
|
|
|
This hierarchy can be expressed as the following dictionary table.
|
|
|
|
| region_id | parent_region | region_name |
|
|
|------------|----------------|---------------|
|
|
| 1 | 0 | Russia |
|
|
| 2 | 1 | Moscow |
|
|
| 3 | 2 | Center |
|
|
| 4 | 0 | Great Britain |
|
|
| 5 | 4 | London |
|
|
|
|
This table contains a column `parent_region` that contains the key of the nearest parent for the element.
|
|
|
|
ClickHouse supports the [hierarchical](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#hierarchical-dict-attr) property for [external dictionary](../../../sql-reference/dictionaries/external-dictionaries/index.md) attributes. This property allows you to configure the hierarchical dictionary similar to described above.
|
|
|
|
The [dictGetHierarchy](../../../sql-reference/functions/ext-dict-functions.md#dictgethierarchy) function allows you to get the parent chain of an element.
|
|
|
|
For our example, the structure of dictionary can be the following:
|
|
|
|
``` xml
|
|
<dictionary>
|
|
<structure>
|
|
<id>
|
|
<name>region_id</name>
|
|
</id>
|
|
|
|
<attribute>
|
|
<name>parent_region</name>
|
|
<type>UInt64</type>
|
|
<null_value>0</null_value>
|
|
<hierarchical>true</hierarchical>
|
|
</attribute>
|
|
|
|
<attribute>
|
|
<name>region_name</name>
|
|
<type>String</type>
|
|
<null_value></null_value>
|
|
</attribute>
|
|
|
|
</structure>
|
|
</dictionary>
|
|
```
|
|
|