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2.8 KiB
2.8 KiB
Dictionary
The Dictionary engine displays the dictionary data as a ClickHouse table.
As an example, consider a dictionary of products with the following configuration:
<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>
Query the dictionary data:
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 │
└──────────┴──────┴────────┴─────────────────┴─────────────────┴─────────────────┴───────────────┴─────────────────┘
You can use the dictGet* function to get the dictionary data in this format.
This view isn’t helpful when you need to get raw data, or when performing a JOIN operation. For these cases, you can use the Dictionary engine, which displays the dictionary data in a table.
Syntax:
CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`
Usage example:
create table products (product_id UInt64, title String) Engine = Dictionary(products);
Ok
Take a look at what’s in the table.
select * from products limit 1;
┌────product_id─┬─title───────────┐
│ 152689 │ Some item │
└───────────────┴─────────────────┘