mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-17 05:03:20 +00:00
7170f3c534
* prefer relative links from root * wip * split aggregate function reference * split system tables
98 lines
2.9 KiB
Markdown
98 lines
2.9 KiB
Markdown
---
|
||
toc_priority: 35
|
||
toc_title: Dictionary
|
||
---
|
||
|
||
# Dictionary Table Engine {#dictionary}
|
||
|
||
The `Dictionary` engine displays the [dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts.md) data as a ClickHouse table.
|
||
|
||
## Example {#example}
|
||
|
||
As an example, consider a dictionary of `products` with the following configuration:
|
||
|
||
``` xml
|
||
<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:
|
||
|
||
``` sql
|
||
SELECT
|
||
name,
|
||
type,
|
||
key,
|
||
attribute.names,
|
||
attribute.types,
|
||
bytes_allocated,
|
||
element_count,
|
||
source
|
||
FROM system.dictionaries
|
||
WHERE name = 'products'
|
||
```
|
||
|
||
``` text
|
||
┌─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\*](../../../sql-reference/functions/ext-dict-functions.md#ext_dict_functions) 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:
|
||
|
||
``` sql
|
||
CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`
|
||
```
|
||
|
||
Usage example:
|
||
|
||
``` sql
|
||
create table products (product_id UInt64, title String) Engine = Dictionary(products);
|
||
```
|
||
|
||
Ok
|
||
|
||
Take a look at what’s in the table.
|
||
|
||
``` sql
|
||
select * from products limit 1;
|
||
```
|
||
|
||
``` text
|
||
┌────product_id─┬─title───────────┐
|
||
│ 152689 │ Some item │
|
||
└───────────────┴─────────────────┘
|
||
```
|
||
|
||
[Original article](https://clickhouse.tech/docs/en/operations/table_engines/dictionary/) <!--hide-->
|