MariaDB 10.0.X中，动态列支持 JSON 格式来获取数据。

MariaDB 10.0.X中，动态列（Dynamic Columns），可以支持 JSON 格式来获取数据。

为了兼容传统SQL语法，MariaDB 10和MySQL5.7支持原生JSON格式，即关系型数据库和文档型NoSQL数据库集于一身。

使用说明：

###表结构

create table assets (  item_name varchar(32) primary key, -- A common attribute for all items  dynamic_cols  blob  -- Dynamic columns will be stored here);

###插入JSON格式数据

mysql> INSERT INTO assets VALUES     ->   ('MariaDB T-shirt', COLUMN_CREATE('color', 'blue', 'size', 'XL'));Query OK, 1 row affected (0.02 sec)mysql> INSERT INTO assets VALUES    ->   ('Thinkpad Laptop', COLUMN_CREATE('color', 'black', 'price', 500));Query OK, 1 row affected (0.01 sec)

###获取Key（键）color的Value（值）：

mysql> SELECT item_name, COLUMN_GET(dynamic_cols, 'color' as char) AS color FROM assets;+-----------------+-------+| item_name       | color |+-----------------+-------+| MariaDB T-shirt | blue  || Thinkpad Laptop | black |+-----------------+-------+2 rows in set (0.00 sec)

###获取全部Key（键）

mysql> SELECT item_name, column_list(dynamic_cols) FROM assets;+-----------------+---------------------------+| item_name       | column_list(dynamic_cols) |+-----------------+---------------------------+| MariaDB T-shirt | `size`,`color`            || Thinkpad Laptop | `color`,`price`           |+-----------------+---------------------------+2 rows in set (0.00 sec)

###获取全部Key-Value

mysql> SELECT item_name, COLUMN_JSON(dynamic_cols) FROM assets;+-----------------+-------------------------------+| item_name       | COLUMN_JSON(dynamic_cols)     |+-----------------+-------------------------------+| MariaDB T-shirt | {"size":"XL","color":"blue"}  || Thinkpad Laptop | {"color":"black","price":500} |+-----------------+-------------------------------+2 rows in set (0.01 sec)

###删除一个Key-Value：

mysql> UPDATE assets SET dynamic_cols=COLUMN_DELETE(dynamic_cols, "price")     -> WHERE COLUMN_GET(dynamic_cols, 'color' as char)='black';Query OK, 1 row affected (0.00 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> SELECT item_name, COLUMN_JSON(dynamic_cols) FROM assets;+-----------------+------------------------------+| item_name       | COLUMN_JSON(dynamic_cols)    |+-----------------+------------------------------+| MariaDB T-shirt | {"size":"XL","color":"blue"} || Thinkpad Laptop | {"color":"black"}            |+-----------------+------------------------------+2 rows in set (0.00 sec)

###增加一个Key-Value：

mysql> UPDATE assets SET dynamic_cols=COLUMN_ADD(dynamic_cols, 'warranty', '3 years')    -> WHERE item_name='Thinkpad Laptop';Query OK, 1 row affected (0.01 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> SELECT item_name, COLUMN_JSON(dynamic_cols) FROM assets;                            +-----------------+----------------------------------------+| item_name       | COLUMN_JSON(dynamic_cols)              |+-----------------+----------------------------------------+| MariaDB T-shirt | {"size":"XL","color":"blue"}           || Thinkpad Laptop | {"color":"black","warranty":"3 years"} |+-----------------+----------------------------------------+2 rows in set (0.00 sec)

###更改一个Key-Value：

mysql> UPDATE assets SET dynamic_cols=COLUMN_ADD(dynamic_cols,'color', 'white') WHERE COLUMN_GET(dynamic_cols, 'color' as char)='black';Query OK, 1 row affected (0.01 sec)Rows matched: 1  Changed: 1  Warnings: 0mysql> SELECT item_name, COLUMN_JSON(dynamic_cols) FROM assets;+-----------------+----------------------------------------+| item_name       | COLUMN_JSON(dynamic_cols)              |+-----------------+----------------------------------------+| MariaDB T-shirt | {"size":"XL","color":"blue"}           || Thinkpad Laptop | {"color":"white","warranty":"3 years"} |+-----------------+----------------------------------------+2 rows in set (0.00 sec)