mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-17 13:13:36 +00:00
0a4a5b36cc
* Additional .gitignore entries * Merge a bunch of small articles about system tables into single one * Merge a bunch of small articles about formats into single one * Adapt table with formats to English docs too * Add SPb meetup link to main page * Move Utilities out of top level of docs (the location is probably not yet final) + translate couple articles * Merge MacOS.md into build_osx.md * Move Data types higher in ToC * Publish changelog on website alongside documentation * Few fixes for en/table_engines/file.md * Use smaller header sizes in changelogs * Group up table engines inside ToC * Move table engines out of top level too * Specificy in ToC that query language is SQL based. Thats a bit excessive, but catches eye. * Move stuff that is part of query language into respective folder * Move table functions lower in ToC * Lost redirects.txt update * Do not rely on comments in yaml + fix few ru titles * Extract major parts of queries.md into separate articles * queries.md has been supposed to be removed * Fix weird translation * Fix a bunch of links * There is only table of contents left * "Query language" is actually part of SQL abbreviation * Change filename in README.md too * fix mistype
3.0 KiB
3.0 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';
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);
CREATE TABLE products
(
product_id UInt64,
title String,
)
ENGINE = Dictionary(products)
Ok.
0 rows in set. Elapsed: 0.004 sec.
Take a look at what's in the table.
select * from products limit 1;
SELECT *
FROM products
LIMIT 1
┌────product_id─┬─title───────────┐
│ 152689 │ Some item │
└───────────────┴─────────────────┘
1 rows in set. Elapsed: 0.006 sec.