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: 0
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"} |
+-----------------+------------------------------+
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: 0
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","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: 0
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":"white","warranty":"3 years"} |
+-----------------+----------------------------------------+
2 rows in set (0.00 sec)
