mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-03 13:02:00 +00:00
112 lines
3.1 KiB
Markdown
112 lines
3.1 KiB
Markdown
|
|
# Dictionary
|
|
|
|
`Dictionary` 引擎将字典数据展示为一个ClickHouse的表。
|
|
|
|
例如，考虑使用一个具有以下配置的 `products` 字典：
|
|
|
|
```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>
|
|
```
|
|
|
|
查询字典中的数据：
|
|
|
|
``` sql
|
|
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 │
|
|
└──────────┴──────┴────────┴─────────────────┴─────────────────┴─────────────────┴───────────────┴─────────────────┘
|
|
```
|
|
|
|
你可以使用 [dictGet*](../../query_language/functions/ext_dict_functions.md) 函数来获取这种格式的字典数据。
|
|
|
|
当你需要获取原始数据，或者是想要使用 `JOIN` 操作的时候，这种视图并没有什么帮助。对于这些情况，你可以使用 `Dictionary` 引擎，它可以将字典数据展示在表中。
|
|
|
|
语法：
|
|
|
|
```
|
|
CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`
|
|
```
|
|
|
|
示例：
|
|
|
|
``` sql
|
|
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.
|
|
```
|
|
|
|
看一看表中的内容。
|
|
|
|
``` sql
|
|
select * from products limit 1;
|
|
|
|
SELECT *
|
|
FROM products
|
|
LIMIT 1
|
|
```
|
|
|
|
```
|
|
┌────product_id─┬─title───────────┐
|
|
│ 152689 │ Some item │
|
|
└───────────────┴─────────────────┘
|
|
|
|
1 rows in set. Elapsed: 0.006 sec.
|
|
```
|
|
|
|
|
|
[来源文章](https://clickhouse.yandex/docs/en/operations/table_engines/dictionary/) <!--hide-->
|