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* CLICKHOUSE-4063: less manual html @ index.md

* CLICKHOUSE-4063: recommend markdown="1" in README.md

* CLICKHOUSE-4003: manually purge custom.css for now

* CLICKHOUSE-4064: expand <details> before any print (including to pdf)

* CLICKHOUSE-3927: rearrange interfaces/formats.md a bit

* CLICKHOUSE-3306: add few http headers

* Remove copy-paste introduced in #3392

* Hopefully better chinese fonts #3392

* get rid of tabs @ custom.css

* Apply comments and patch from #3384

* Add jdbc.md to ToC and some translation, though it still looks badly incomplete

* minor punctuation

* Add some backlinks to official website from mirrors that just blindly take markdown sources

* Do not make fonts extra light

* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {}

* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {}

* Remove outdated stuff from roadmap.md

* Not so light font on front page too

* Refactor Chinese formats.md to match recent changes in other languages

2018-10-16 13:47:17 +03:00

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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.

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Dictionary

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