MySQL5.7特性：JSON数据类型

MySQL5.7特性：jsON数据类型

概述

MySQL5.7的发行声明中，官方称之为里程碑式的版本，除了运行速度大幅度提升之外，还添加了之前版本没有的功能，如本文所述的原生JSON数据类型功能。

在此版本之前，MySQL所有的JSON数据类型，全部是使用text等文本类型来实现的，数据的处理只能在应用代码级来实现，十分不方便。

什么是JSON类型

作为DBA，可能会对这个概念稍微有点陌生，但是对于开发者来说，这是一个十分熟悉的事物。

JSON(JavaScript Object Notation, JS 对象简谱) 是一种轻量级的数据交换格式。它基于 ECMAScript (欧洲计算机协会制定的js规范)的一个子集，采用完全独立于编程语言的文本格式来存储和表示数据。简洁和清晰的层次结构使得 JSON 成为理想的数据交换语言。 易于人阅读和编写，同时也易于机器解析和生成，并有效地提升网络传输效率。

MySQL原始JSON类型的优势在哪？

原生的JSON优势如下：

存储上类似text,可以存非常大的数据。

存储在JSON列中的JSON文档的自动验证 。无效的文档会产生错误。

优化的存储格式。存储在JSON列中的JSON文档将 转换为内部格式，以允许对文档元素进行快速读取访问。

相比于传统形式，不需要遍历所有字符串才能找到数据。

支持索引：通过虚拟列的功能可以对JSON中部分的数据进行索引。

MySQL的JSON类型

创建JSON类型表

创建一个基础的员工表，除了工号字段外，还有一个个人基础信息字段和一个个人能力信息字段

MySQL [test]> CREATE TABLE employee (

->

-> `empno` int(10) unsigned NOT NULL AUTO_INCREMENT,

->

-> `basic_info` JSON NOT NULL,

->

-> `skill_info` JSON NOT NULL,

->

-> PRIMARY KEY (`empno`)

->

-> );

Query OK, 0 rows affected (0.02 sec)

表的基础信息，其中JSON类型的字段，是不可以有默认值的，这点需要注意

MySQL [test]> desc employee;

+------------+------------------+------+-----+---------+----------------+

| Field | Type | Null | Key | Default | Extra |

+------------+------------------+------+-----+---------+----------------+

| empno | int(10) unsigned | NO | PRI | NULL | auto_increment |

| basic_info | json | NO | | NULL | |

| skill_info | json | NO | | NULL | |

+------------+------------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

试着插入几条数据

我们手动插入几条数据进这张表中，在前两条数据中，在个人能力信息上使用的是数组的方式，后面两条则是使用对象的形式。在MySQL5.7.8版本后的JSON类型中，这两种都是可以的。

INSERT INTO `employee` VALUES (1,'{"name": "wangyiyi", "age": "23" ,"from": "hangzhou"}', '["java", "go", "python"]');

INSERT INTO `employee` VALUES (2,'{"name": "linxue", "age": 24 ,"from": "shanghai"}', '["mysql", "oracle", "python"]');

INSERT INTO `employee` VALUES (3,'{"name": "zhaoqing", "age": 24 ,"from": "shanghai"}', '{"system": "linux","database": "mysql", "language": "python"}');

INSERT INTO `employee` VALUES (4,'{"name": "zhouxixi", "age": 30 ,"from": "nanjing"}', '{"system": ["linux","windows"],"database": ["mysql","oracle","postgresql"], "language": ["python","java","go"]}');

插入多个数据后,表中内容为如下

MySQL [test]> select * from employee;

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

| 1 | {"age": "23", "from": "hangzhou", "name": "wangyiyi"} | ["java", "go", "python"] |

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

| 3 | {"age": 24, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "python"} |

| 4 | {"age": 30, "from": "nanjing", "name": "zhouxixi"} | {"system": ["linux", "windows"], "database": ["mysql", "oracle", "postgresql"], "language": ["python", "java", "go"]} |

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

4 rows in set (0.00 sec)

json数据查询方式

在插入了json类型的数据之后，可以针对JSON类型做一些特定的查询，如查询年龄大于20的记录

在SQL的语句中使用 字段->键名 就可以查询出所对应的键值

MySQL [test]> select * from employee WHERE basic_info->'$.age'> 20;

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

| 1 | {"age": "23", "from": "hangzhou", "name": "wangyiyi"} | ["java", "go", "python"] |

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

| 3 | {"age": 28, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "go"} |

| 4 | {"age": 30, "from": "nanjing", "name": "zhouxixi"} | {"system": ["linux", "windows"], "database": ["mysql", "oracle", "postgresql"], "language": ["python", "java", "go"]} |

+-------+-------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------+

4 rows in set (0.00 sec)

MySQL [test]> select * from employee WHERE basic_info->'$.age'< 20;

Empty set (0.00 sec)

除了使用上述方式外，也可使用 提取json值的 函数 json_extract （使用函数的方式）

MySQL [test]> select * from employee where json_extract(basic_info,'$.age') = 24;

+-------+-----------------------------------------------------+----------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-----------------------------------------------------+----------------------------------------------------------------+

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

| 3 | {"age": 24, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "python"} |

+-------+-----------------------------------------------------+----------------------------------------------------------------+

2 rows in set (0.00 sec)

对于数值查询也可做一个范围内查询，如下：

MySQL [test]> select * from employee WHERE basic_info->'$.age' in (23, 24);

+-------+-------------------------------------------------------+----------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-------------------------------------------------------+----------------------------------------------------------------+

| 1 | {"age": "23", "from": "hangzhou", "name": "wangyiyi"} | ["java", "go", "python"] |

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

| 3 | {"age": 24, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "python"} |

+-------+-------------------------------------------------------+----------------------------------------------------------------+

3 rows in set, 1 warning (0.00 sec)

因为 JSON 不同于字符串，所以如果用字符串和 JSON 字段比较，是不会相等的；

如下，直接使用字符串查询，查询不出来内容

MySQL [test]> select * from employee where basic_info = '{"age": 24, "from": "shanghai", "name": "linxue"}';

Empty set (0.00 sec)

可以通过 CAST 将字符串转成 JSON 的形式，如下：

MySQL [test]> select * from employee where basic_info = CAST('{"age": 24, "from": "shanghai", "name": "linxue"}' AS JSON);

+-------+---------------------------------------------------+-------------------------------+

| empno | basic_info | skill_info |

+-------+---------------------------------------------------+-------------------------------+

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

+-------+---------------------------------------------------+-------------------------------+

1 row in set (0.00 sec)

查看单纯数组类型的函数JSON_CONTAINS

MySQL [test]> select * from employee where JSON_CONTAINS (skill_info,'"mysql"');

+-------+---------------------------------------------------+-------------------------------+

| empno | basic_info | skill_info |

+-------+---------------------------------------------------+-------------------------------+

| 2 | {"age": 24, "from": "shanghai", "name": "linxue"} | ["mysql", "oracle", "python"] |

+-------+---------------------------------------------------+-------------------------------+

1 row in set (0.00 sec)

JSON_PRETTY函数： 以易于阅读的格式打印出JSON值。便于在一些外部应用引用数据时，更方便的使用它

MySQL [test]> select JSON_PRETTY(basic_info) from employee;

+---------------------------------------------------------------+

| JSON_PRETTY(basic_info) |

+---------------------------------------------------------------+

| {

"age": "23",

"from": "hangzhou",

"name": "wangyiyi"

} |

| {

"age": 24,

"from": "shanghai",

"name": "linxue"

} |

| {

"age": 28,

"from": "shanghai",

"name": "zhaoqing"

} |

| {

"age": 30,

"from": "nanjing",

"name": "zhouxixi"

} |

+---------------------------------------------------------------+

4 rows in set (0.00 sec)

MySQL 5.7.22中添加了此功能，此函数返回用于存储JSON文档的二进制表示的字节数，用于查看当前JSON字段的存储大小

MySQL [test]> select skill_info,JSON_STORAGE_SIZE(skill_info) AS Size from employee;

+-----------------------------------------------------------------------------------------------------------------------+------+

| skill_info | Size |

+-----------------------------------------------------------------------------------------------------------------------+------+

| ["java", "go", "python"] | 29 |

| ["mysql", "oracle", "python"] | 34 |

| {"system": "linux", "database": "mysql", "language": "go"} | 63 |

| {"system": ["linux", "windows"], "database": ["mysql", "oracle", "postgresql"], "language": ["python", "java", "go"]} | 137 |

+-----------------------------------------------------------------------------------------------------------------------+------+

4 rows in set (0.00 sec)

查询JSON字段的长度

MySQL [test]> select JSON_LENGTH(basic_info) from employee;

+-------------------------+

| JSON_LENGTH(basic_info) |

+-------------------------+

| 3 |

| 3 |

| 3 |

| 3 |

+-------------------------+

4 rows in set (0.00 sec)

查看数据的类型：可以是对象，数组或标量类型

MySQL [test]> select JSON_TYPE(skill_info) from employee;

+-----------------------+

| JSON_TYPE(skill_info) |

+-----------------------+

| ARRAY |

| ARRAY |

| OBJECT |

| OBJECT |

+-----------------------+

4 rows in set (0.00 sec)

json数据修改方式

如果是整个 json 更新的话，和一般类型插入是一样的

json_array_insert是在指定下标插入，这是插入一般数组类型时的操作

MySQL [test]> SELECT json_array_insert(skill_info, '$[1]', 'php') from employee;

+-----------------------------------------------------------------------------------------------------------------------+

| json_array_insert(skill_info, '$[1]', 'php') |

+-----------------------------------------------------------------------------------------------------------------------+

| ["java", "php", "go", "python"] |

| ["mysql", "php", "oracle", "python"] |

| {"system": "linux", "database": "mysql", "language": "python"} |

| {"system": ["linux", "windows"], "database": ["mysql", "oracle", "postgresql"], "language": ["python", "java", "go"]} |

+-----------------------------------------------------------------------------------------------------------------------+

4 rows in set (0.00 sec)

替换操作，也就是修改update操作，使用的是 json_replace 函数

json_replace：只替换已经存在的旧值，不存在则忽略；

MySQL [test]> update employee set skill_info = json_replace(skill_info, "$.language", "go") where empno = 3;

Query OK, 1 row affected (0.00 sec)

Rows matched: 1 Changed: 1 Warnings: 0

MySQL [test]> select * from employee where empno = 3;

+-------+-----------------------------------------------------+------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-----------------------------------------------------+------------------------------------------------------------+

| 3 | {"age": 24, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "go"} |

+-------+-----------------------------------------------------+------------------------------------------------------------+

1 row in set (0.00 sec)

json_set：替换旧值，并插入不存在的新值；

MySQL [test]> update employee set basic_info = json_set(basic_info, "$.age", 28,"$.sex" ,"man") where empno = 3;

Query OK, 1 row affected (0.01 sec)

Rows matched: 1 Changed: 1 Warnings: 0

MySQL [test]>

MySQL [test]> select * from employee where empno = 3;

+-------+-------------------------------------------------------------------+------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-------------------------------------------------------------------+------------------------------------------------------------+

| 3 | {"age": 28, "sex": "man", "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "go"} |

+-------+-------------------------------------------------------------------+------------------------------------------------------------+

1 row in set (0.00 sec)

json_insert：插入新值，但不替换已经存在的旧值；

MySQL [test]> update employee set basic_info = json_insert (basic_info, "$.age", 30, "$.phone" ,"123456789") where empno = 3;

Query OK, 1 row affected (0.01 sec)

Rows matched: 1 Changed: 1 Warnings: 0

MySQL [test]> select * from employee where empno = 3;

+-------+-----------------------------------------------------------------------------------------+------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-----------------------------------------------------------------------------------------+------------------------------------------------------------+

| 3 | {"age": 28, "sex": "man", "from": "shanghai", "name": "zhaoqing", "phone": "123456789"} | {"system": "linux", "database": "mysql", "language": "go"} |

+-------+-----------------------------------------------------------------------------------------+------------------------------------------------------------+

1 row in set (0.00 sec)

json_remove() 删除元素函数。

MySQL [test]> update employee set basic_info = json_remove (basic_info, "$.sex", "$.phone") where empno = 3;

Query OK, 1 row affected (0.01 sec)

Rows matched: 1 Changed: 1 Warnings: 0

MySQL [test]>

MySQL [test]> select * from employee where empno = 3;

+-------+-----------------------------------------------------+------------------------------------------------------------+

| empno | basic_info | skill_info |

+-------+-----------------------------------------------------+------------------------------------------------------------+

| 3 | {"age": 28, "from": "shanghai", "name": "zhaoqing"} | {"system": "linux", "database": "mysql", "language": "go"} |

+-------+-----------------------------------------------------+------------------------------------------------------------+

1 row in set (0.00 sec)

结语

JSON数据类型是一个对开发十分友好的功能，有了它，MySQL的功能才更趋于完善。

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