MySQL5.7 JSON类型及其相关函数的学习

mysql> CREATE TABLE `json_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `info` json NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

mysql> select * from json_table ;
+----+------------------------------+
| id | info                         |
+----+------------------------------+
|  1 | {"age": 24, "name": "lucy"}  |
|  2 | {"age": 20, "name": "lili"}  |
|  3 | {"age": 25, "name": "curry"} |
+----+------------------------------+
3 rows in set (0.00 sec)

Creating JSON Values

MySQL里的json分为json array和json object。

• JSON_TYPE()：查看字段类型

• JSON_ARRAY()：返回json数组

• JSON_OBJECT()：返回json对象

• JSON_MERGE()：合并多个json文档

举个栗子：

#查看类型
mysql> select id, json_extract(info, '$.name') as name , json_type(json_extract(info, '$.name')) as type from json_table where id=3 ;  
+----+---------+--------+
| id | name    | type   |
+----+---------+--------+
|  3 | "curry" | STRING |
+----+---------+--------+
1 row in set (0.00 sec)

#生成一个json数据组
mysql> select json_array('aaa', 'bbb', 'ddd') as array;
+-----------------------+
| array                 |
+-----------------------+
| ["aaa", "bbb", "ddd"] |
+-----------------------+
1 row in set (0.00 sec)

#生成一个json对象
mysql> select json_object('aaa', 1, 'bbb', 2, 'ddd', 3) as array;
+--------------------------------+
| array                          |
+--------------------------------+
| {"aaa": 1, "bbb": 2, "ddd": 3} |
+--------------------------------+
1 row in set (0.00 sec)

#将多个json文档合并
mysql> select json_merge(json_array('aaa', 'bbb', 'ddd'), json_object('aaa', 1, 'bbb', 2, 'ddd', 3))  as json ;
+-------------------------------------------------------+
| json                                                  |
+-------------------------------------------------------+
| ["aaa", "bbb", "ddd", {"aaa": 1, "bbb": 2, "ddd": 3}] |
+-------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

JSON查询

MySQL里的json分为json array和json object
对于json array，在索引数据时用从0开始的下标进行索引，$表示整个json对象，例如：$[0]、$[1]
对于json object，在索引数据时用key进行索引，含有特殊字符的key要用""括起来，比如$."my name")

• 提取json字段：json列->'$.键' 或 JSON_EXTRACT(json列 , '$.键')

• 去掉json字段双引号：JSON_UNQOUTE() 或者 json列->>'$.键'

提取JSON 字段的表达式可以用于SELECT查询列表 ，WHERE/HAVING , ORDER/GROUP BY语句中，JSON 中的元素搜索也是严格区分变量类型

json不同于字符串，不能当作字符串直接做比较，通过CAST()将字符串转换成JSON形式，再进行比较，后面举栗

举个栗子：

json列->'$.键' 查询：

mysql> select id, info->'$.name' as name from json_table ;
+----+---------+
| id | name    |
+----+---------+
|  1 | "lucy"  |
|  2 | "lili"  |
|  3 | "curry" |
+----+---------+
3 rows in set (0.00 sec)

mysql> select id, info->'$.name' as name from json_table where info->'$.age' >=24;
+----+---------+
| id | name    |
+----+---------+
|  1 | "lucy"  |
|  3 | "curry" |
+----+---------+
2 rows in set (0.00 sec)

##复杂情况下的查询，例如
mysql> select   info from json_table where id=3;
+----------------------------------------------------------------+
| info                                                           |
+----------------------------------------------------------------+
| ["abc", {"xxx": [123, 456], "my key": "my value"}, [666, 100]] |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

## 查询json array的某个值
mysql> select info->'$[0]' from json_table where id=3 ;
+---------------+
| info->'$[0]'  |
+---------------+
| "abc"          |
+---------------+
1 row in set (0.00 sec)

## 查询json array中的的json object
mysql> select info->'$[1]."my key"' from json_table where id=3 ;
+--------------------------+
| info->'$[1]."my key"' |
+--------------------------+
| "my value"               |
+--------------------------+
1 row in set (0.00 sec)

JSON_EXTRACT(json列 , '$.键')查询：

mysql> select id, json_extract(info, '$.name') as name from json_table ;
+----+---------+
| id | name    |
+----+---------+
|  1 | "lucy"  |
|  2 | "lili"  |
|  3 | "curry" |
+----+---------+
3 rows in set (0.05 sec)

mysql> select id, json_extract(info, '$.name') as name from json_table where json_extract(info, '$.age') >= 24; 
+----+---------+
| id | name    |
+----+---------+
|  1 | "lucy"  |
|  3 | "curry" |
+----+---------+
2 rows in set (0.00 sec)

JSON_UNQOUTE()方法举栗：

mysql> select id, json_unquote(json_extract(info, '$.name')) as name from json_table ;
+----+-------+
| id | name  |
+----+-------+
|  1 | lucy  |
|  2 | lili  |
|  3 | curry |
+----+-------+
3 rows in set (0.00 sec)

mysql> select id, info->>'$.name' as name from json_table ;
+----+-------+
| id | name  |
+----+-------+
|  1 | lucy  |
|  2 | lili  |
|  3 | curry |
+----+-------+
3 rows in set (0.00 sec)

JSON字段与字符串比较举栗：

mysql> select * from json_table where info = '{"age": 25, "name": "curry"}';
Empty set (0.00 sec)

mysql> select * from json_table where info = cast('{"age": 25, "name": "curry"}' as JSON);
+----+------------------------------+
| id | info                         |
+----+------------------------------+
|  3 | {"age": 25, "name": "curry"} |
+----+------------------------------+
1 row in set (0.00 sec)

JSON的索引

现在MySQL不支持对JSON列进行索引，官网文档的说明是：

JSON columns cannot be indexed. You can work around this restriction by creating an index on a generated column that extracts a scalar value from the JSON column.

虽然不支持直接在JSON列上建索引，但MySQL规定，可以首先使用路径表达式对JSON文档中的标量值建立虚拟列，然后在虚拟列上建立索引。这样用户可以使用表达式对自己感兴趣的键值建立索引。

栗如，创建索引：

mysql> alter table json_table add name varchar(20) generated always as (info->'$.name') virtual ;
Query OK, 0 rows affected (0.35 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from json_table ;
+----+------------------------------+---------+
| id | info                         | name    |
+----+------------------------------+---------+
|  1 | {"age": 24, "name": "lucy"}  | "lucy"  |
|  2 | {"age": 20, "name": "lili"}  | "lili"  |
|  3 | {"age": 25, "name": "curry"} | "curry" |
|  4 | {"age": 24, "name": "tom"}   | "tom"   |
|  5 | {"age": 24, "name": "jurry"} | "jurry" |
|  6 | {"age": 30, "name": "tmry"}  | "tmry"  |
+----+------------------------------+---------+
6 rows in set (0.00 sec)

mysql> select * from json_table where name=""tom"";
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'tom""' at line 1
mysql> select * from json_table where name=""tom"";
+----+----------------------------+-------+
| id | info                       | name  |
+----+----------------------------+-------+
|  4 | {"age": 24, "name": "tom"} | "tom" |
+----+----------------------------+-------+
1 row in set (0.00 sec)
mysql> alter table json_table add index name_idx(name) ;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table json_table G
*************************** 1. row ***************************
       Table: json_table
Create Table: CREATE TABLE `json_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `info` json NOT NULL,
  `name` varchar(20) GENERATED ALWAYS AS (json_extract(`info`,'$.name')) VIRTUAL,
  PRIMARY KEY (`id`),
  KEY `name_idx` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> alter table json_table rename index name_idx to idx_name ;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table json_table G                           
*************************** 1. row ***************************
       Table: json_table
Create Table: CREATE TABLE `json_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `info` json NOT NULL,
  `name` varchar(20) GENERATED ALWAYS AS (json_extract(`info`,'$.name')) VIRTUAL,
  PRIMARY KEY (`id`),
  KEY `idx_name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

修改

JSON_INSERT() 插入新字段，对于已存在的字段无法修改

#插入新字段
mysql> update json_table set info=json_insert(info, '$.sex', 'M');
Query OK, 6 rows affected (0.30 sec)
Rows matched: 6  Changed: 6  Warnings: 0

mysql> select * from json_table ;  
+----+-----------------------------------------------------------+
| id | info                                                      |
+----+-----------------------------------------------------------+
|  1 | {"age": 24, "sex": "M", "name": "lucy"}                   |
|  2 | {"age": 20, "sex": "M", "name": "lili"}                   |
|  3 | {"age": 25, "sex": "M", "name": "curry"}                  |
|  4 | {"age": 24, "sex": "M", "name": "tom"}                    |
|  5 | {"age": 24, "sex": "M", "name": "jurry"}                  |
|  6 | {"age": 30, "sex": "M", "name": "tmry"}                   |
+----+-----------------------------------------------------------+
6 rows in set (0.00 sec)

#对于已存在的字段无法修改
mysql> update json_table set info=json_insert(info, '$.name', 'LUCY') where id=1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

mysql> select * from json_table where id=1 ;                                               
+----+-----------------------------------------------------------+
| id | info                                                      |
+----+-----------------------------------------------------------+
|  1 | {"age": 24, "sex": "M", "name": "lucy"}                   |
+----+-----------------------------------------------------------+
6 rows in set (0.00 sec)

JSON_SET() 插入新值字段，并覆盖已经存在字段的值

#覆盖已经存在字段的值
mysql> update json_table set info=json_set(info, '$.name', 'LUCY') where id=1;       
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from json_table where id=1;                                  
+----+-----------------------------------------------------------+
| id | info                                                      |
+----+-----------------------------------------------------------+
|  1 | {"age": 24, "sex": "M", "name": "LUCY"}                   |
+----+-----------------------------------------------------------+
1 row in set (0.00 sec)

#插入新值字段
mysql> update json_table set info=json_set(info, '$.class', 'python') where id=2;         
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from json_table where id=2;                                     
+----+------------------------------------------------------------+
| id | info                                                       |
+----+------------------------------------------------------------+
|  2 | {"age": 20, "sex": "M", "name": "lili", "class": "python"} |
+----+------------------------------------------------------------+
1 row in set (0.00 sec)

JSON_REPLACE() 只替换存在的字段

mysql> update json_table set info=json_replace(info, '$.sex', 'W') where id=2;     
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select *  from json_table where id = 2 ; 
+----+------------------------------------------------------------+
| id | info                                                       |
+----+------------------------------------------------------------+
|  2 | {"age": 20, "sex": "W", "name": "lili", "class": "python"} |
+----+------------------------------------------------------------+
1 row in set (0.00 sec)

JSON_REMOVE() 删除 JSON 元素

mysql> update json_table set info=json_remove(info, '$.class') where id=2 ;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select *  from json_table where id = 2 ;                            
+----+-----------------------------------------+
| id | info                                    |
+----+-----------------------------------------+
|  2 | {"age": 20, "sex": "W", "name": "lili"} |
+----+-----------------------------------------+
1 row in set (0.00 sec)