:original_name: ddm_10_0013.html

.. _ddm_10_0013:

Range
=====

Application Scenarios
---------------------

This algorithm applies to routing data in different ranges to different shards. Less-than signs (<), greater-than signs (>), and BETWEEN ... AND ... are frequently used in SQL queries.

Instructions
------------

The sharding key can only be an integer, a date, or used in combination with a date function. If a date function is used, the sharding key must be DATE, DATETIME, or TIMESTAMP.

Data Routing
------------

Data is routed to different shards by the sharding key value based on algorithm metadata rules.

Metadata needs to be set when a table is created. For example, if there are eight shards in one schema, the metadata range can be 1-2=0, 3-4=1, 5-6=2, 7-8=3, 9-10=4, 11-12=5, 13-14=6, and default=7. Data is routed to shards by the sharding key value based on the range.

Calculation Method
------------------

**Method 1: Use an Integer as the Sharding Key**

.. table:: **Table 1** Required calculation methods when the sharding key is the integer data type

   +-----------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
   | Condition             | Calculation Method                                                                                                   | Example                                                                                       |
   +=======================+======================================================================================================================+===============================================================================================+
   | Integer sharding keys | Database routing result: Data is routed to different shards based on the sharding key and the preset metadata range. | Data is routed to shard1 if the sharding key value is 3 and the preset metadata range is 3-4. |
   +-----------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+

**Method 2: Use a Date as the Sharding Key**

.. table:: **Table 2** Supported date functions

   +---------------+--------------------------------------------------------+------------------------------+
   | Date Function | Calculation Method                                     | Example                      |
   +===============+========================================================+==============================+
   | year()        | year(yyyy-MM-dd)=yyyy                                  | year('2019-10-11')=2019      |
   +---------------+--------------------------------------------------------+------------------------------+
   | month()       | month(yyyy-MM-dd)=MM                                   | month('2019-10-11')=10       |
   +---------------+--------------------------------------------------------+------------------------------+
   | weekofyear()  | weekofyear(yyyy-MM-dd)=Week number of the current year | weekofyear ('2019-10-11')=41 |
   +---------------+--------------------------------------------------------+------------------------------+
   | day()         | day(yyyy-MM-dd)=Day number of the current month        | day ('2019-10-11')=11        |
   +---------------+--------------------------------------------------------+------------------------------+

.. table:: **Table 3** Calculation methods

   +-------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
   | Condition         | Calculation Method                                                                                                                                    | Example                                                                                                                               |
   +===================+=======================================================================================================================================================+=======================================================================================================================================+
   | Date sharding key | Database routing: Data is routed to different database shards based on the date function (database sharding key value) and the preset metadata range. | Data is routed to shard 4 based on the metadata range 9-10 when the sharding key value is 10: month(2019-10-11)=10 belongs to 9-10=4. |
   +-------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+

Syntax for Creating Tables
--------------------------

.. code-block:: text

   create table range_tb(
       id int,
       name varchar(30) DEFAULT NULL,
       create_time datetime DEFAULT NULL,
       primary key(id)
       )
   dbpartition by range(id)
   {
       1-2=0,
       3-4=1,
       5-6=2,
       7-8=3,
       9-10=4,
       11-12=5,
       13-14=6,
       default=7
   };

Precautions
-----------

None