Dictionary Table Engine
The Dictionary
engine displays the dictionary data as a ClickHouse table.
Exampleβ
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'
ββnameββββββ¬βtypeββ¬βkeyβββββ¬βattribute.namesββ¬βattribute.typesββ¬βbytes_allocatedββ¬βelement_countββ¬βsourceβββββββββββ
β products β Flat β UInt64 β ['title'] β ['String'] β 23065376 β 175032 β ODBC: .products β
ββββββββββββ΄βββββββ΄βββββββββ΄ββββββββββββββββββ΄ββββββββββββββββββ΄ββββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββββ
You can use the dictGet* function to get the dictionary data in this format.
This view isnβt 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 whatβs in the table.
select * from products limit 1;
βββββproduct_idββ¬βtitleββββββββββββ
β 152689 β Some item β
βββββββββββββββββ΄ββββββββββββββββββ
See Also