Dictionary Key and Fields

XML description:

Attributes are described in the elements:

<id> — Key column.
<attribute> — . There can be a multiple number of attributes.

DDL query:

CREATE DICTIONARY dict_name (
    Id UInt64,
    -- attributes
)
...

Attributes are described in the query body:

PRIMARY KEY — Key column
AttrName AttrType — . There can be a multiple number of attributes.

ClickHouse supports the following types of keys:

Numeric key. UInt64. Defined in the <id> tag or using PRIMARY KEY keyword.
Composite key. Set of values of different types. Defined in the tag <key> or PRIMARY KEY keyword.

An xml structure can contain either <id> or <key>. DDL-query must contain single PRIMARY KEY.

You must not describe key as an attribute.

Type: UInt64.

Configuration example:

Configuration fields:

name – The name of the column with keys.

For DDL-query:


    Id UInt64,
    ...
)
PRIMARY KEY Id

PRIMARY KEY – The name of the column with keys.

Composite Key

The key can be a tuple from any types of fields. The in this case must be complex_key_hashed or complex_key_cache.

A composite key can consist of a single element. This makes it possible to use a string as the key, for instance.

The key structure is set in the element <key>. Key fields are specified in the same format as the dictionary attributes. Example:

CREATE DICTIONARY (
    field1 String,
    field2 String
    ...
)
PRIMARY KEY field1, field2
...

For a query to the dictGet* function, a tuple is passed as the key. Example: dictGetString('dict_name', 'attr_name', tuple('string for field1', num_for_field2)).

Configuration example:

CREATE DICTIONARY somename (
)