ClickHouse/docs/ru/operations/table_engines/dictionary.md
Ivan Blinkov 0a4a5b36cc
Some WIP on documentation refactoring (#2659)
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2018-07-18 13:00:53 +03:00

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Dictionary

Движок Dictionary отображает данные словаря как таблицу ClickHouse.

Рассмотрим для примера словарь products со следующей конфигурацией:

<dictionaries>
<dictionary>
        <name>products</name>
        <source>
            <odbc>
                <table>products</table>
                <connection_string>DSN=some-db-server</connection_string>
            </odbc>
        </source>
        <lifetime>
            <min>300</min>
            <max>360</max>
        </lifetime>
        <layout>
            <flat/>
        </layout>
        <structure>
            <id>
                <name>product_id</name>
            </id>
            <attribute>
                <name>title</name>
                <type>String</type>
                <null_value></null_value>
            </attribute>
        </structure>
</dictionary>
</dictionaries>

Запрос данных словаря:

select name, type, key, attribute.names, attribute.types, bytes_allocated, element_count,source from system.dictionaries where name = 'products';                     

SELECT
    name,
    type,
    key,
    attribute.names,
    attribute.types,
    bytes_allocated,
    element_count,
    source
FROM system.dictionaries
WHERE name = 'products'
┌─name─────┬─type─┬─key────┬─attribute.names─┬─attribute.types─┬─bytes_allocated─┬─element_count─┬─source──────────┐
│ products │ Flat │ UInt64 │ ['title']       │ ['String']      │        23065376 │        175032 │ ODBC: .products │
└──────────┴──────┴────────┴─────────────────┴─────────────────┴─────────────────┴───────────────┴─────────────────┘

В таком виде данные из словаря можно получить при помощи функций dictGet*.

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.

Синтаксис:

CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`

Пример использования:

create table products (product_id UInt64, title String) Engine = Dictionary(products);

CREATE TABLE products
(
    product_id UInt64,
    title String,
)
ENGINE = Dictionary(products)
Ok.

0 rows in set. Elapsed: 0.004 sec.

Проверим что у нас в таблице?

select * from products limit 1;

SELECT *
FROM products
LIMIT 1
┌────product_id─┬─title───────────┐
│        152689 │ Some item       │
└───────────────┴─────────────────┘

1 rows in set. Elapsed: 0.006 sec.