ClickHouse/docs/zh/operations/table_engines/dictionary.md

<a name="table_engines-dictionary"></a>

# Dictionary

The `Dictionary` engine displays the dictionary data as a ClickHouse table.

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';                     

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*](../../query_language/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:

```
CREATE TABLE %table_name% (%fields%) engine = Dictionary(%dictionary_name%)`
```

Usage example:

``` 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.
```

Take a look at what's in the table.

``` 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.
```


[Original article](https://clickhouse.yandex/docs/en/operations/table_engines/dictionary/) <!--hide-->