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109 lines
3.4 KiB
Markdown
109 lines
3.4 KiB
Markdown
<a name="table_engines-dictionary"></a>
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# Dictionary
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Движок `Dictionary` отображает данные словаря как таблицу ClickHouse.
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Рассмотрим для примера словарь `products` со следующей конфигурацией:
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```xml
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<dictionaries>
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<dictionary>
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<name>products</name>
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<source>
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<odbc>
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<table>products</table>
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<connection_string>DSN=some-db-server</connection_string>
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</odbc>
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</source>
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<lifetime>
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<min>300</min>
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<max>360</max>
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</lifetime>
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<layout>
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<flat/>
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</layout>
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<structure>
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<id>
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<name>product_id</name>
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</id>
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<attribute>
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<name>title</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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</dictionaries>
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```
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Запрос данных словаря:
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```sql
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select name, type, key, attribute.names, attribute.types, bytes_allocated, element_count,source from system.dictionaries where name = 'products';
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SELECT
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name,
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type,
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key,
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attribute.names,
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attribute.types,
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bytes_allocated,
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element_count,
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source
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FROM system.dictionaries
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WHERE name = 'products'
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```
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```
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┌─name─────┬─type─┬─key────┬─attribute.names─┬─attribute.types─┬─bytes_allocated─┬─element_count─┬─source──────────┐
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│ products │ Flat │ UInt64 │ ['title'] │ ['String'] │ 23065376 │ 175032 │ ODBC: .products │
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└──────────┴──────┴────────┴─────────────────┴─────────────────┴─────────────────┴───────────────┴─────────────────┘
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```
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В таком виде данные из словаря можно получить при помощи функций [dictGet*](../../query_language/functions/ext_dict_functions.md#ext_dict_functions).
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Такое представление неудобно, когда нам необходимо получить данные в чистом виде, а также при выполнении операции `JOIN`. Для этих случаев можно использовать движок `Dictionary`, который отобразит данные словаря в таблицу.
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Синтаксис:
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```
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CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`
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```
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Пример использования:
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```sql
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create table products (product_id UInt64, title String) Engine = Dictionary(products);
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CREATE TABLE products
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(
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product_id UInt64,
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title String,
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)
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ENGINE = Dictionary(products)
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```
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```
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Ok.
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0 rows in set. Elapsed: 0.004 sec.
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```
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Проверим что у нас в таблице?
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```sql
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select * from products limit 1;
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SELECT *
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FROM products
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LIMIT 1
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```
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```
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┌────product_id─┬─title───────────┐
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│ 152689 │ Some item │
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└───────────────┴─────────────────┘
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1 rows in set. Elapsed: 0.006 sec.
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```
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