Javascript
MySQL8.0新特性—JSON增强
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要在MySQL中存储数据，就必须定义数据库和表结构(schema)，这是一个主要的限制。为了应对这一点，从MySQL 5.7开始，MySQL支恃了JavaScript对象表示(JavaScriptObject Notation，JSON)数据类型。之前，这类数据不是单独的数据类型，会被存储为字符串。新的JSON数据类型提供了自动验证的JSON文档以及优化的存储格式。
JSON文档以二进制格式存储，它提供以下功能：
- 对文档元素的快速读取访问。
- 当服务器再次读取
JSON文档时，不需要重新解析文本获取该值。 - 通过键或数组索引直接查找子对象或嵌套值，而不需要读取文档中的所有值。
一、创建数据
1.1 创建测试表
mysql> create table employees.emp_details (
-> emp_no int primary key,
-> details json
-> );
Query OK, 0 rows affected (0.17 sec)
mysql> desc employees.emp_details;
+---------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+-------+
| emp_no | int(11) | NO | PRI | NULL | |
| details | json | YES | | NULL | |
+---------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
1.2 插入JSON
mysql> insert into employees.emp_details (emp_no, details)
-> values ('1',
-> '{"location":"IN","phone":"+11800000000","email":"abc@example.com","address":{"line1":"abc","line2":"xyz street","city":"Bangalore","pin":"560103"}}'
-> );
Query OK, 1 row affected (0.13 sec)
mysql> select emp_no, details from employees.emp_details;
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| emp_no | details |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 1 | {"email": "abc@example.com", "phone": "+11800000000", "address": {"pin": "560103", "city": "Bangalore", "line1": "abc", "line2": "xyz street"}, "location": "IN"} |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
1.3 检索JSON
可以使用->和->>运算符检索JSON列的字段：
mysql> select emp_no, details -> '$.address.pin' pin
-> from employees.emp_details;
+--------+----------+
| emp_no | pin |
+--------+----------+
| 1 | "560103" |
+--------+----------+
1 row in set (0.00 sec)
如果不用引号检索数据，可以使用->>运算符（推荐此方式）
mysql> select emp_no, details ->> '$.address.pin' pin
-> from employees.emp_details;
+--------+--------+
| emp_no | pin |
+--------+--------+
| 1 | 560103 |
+--------+--------+
1 row in set (0.00 sec)
二、JSON函数
MySQL提供了许多处理JSON数据的函数，让我们看看最常用的几种函数。
2.1 优雅浏览
想要以优雅的格式显示JSON值，请使用JSON_PRETTY()函数
mysql> select emp_no, json_pretty(details)
-> from employees.emp_details\G
*************************** 1. row ***************************
emp_no: 1
json_pretty(details): {
"email": "abc@example.com",
"phone": "+11800000000",
"address": {
"pin": "560103",
"city": "Bangalore",
"line1": "abc",
"line2": "xyz street"
},
"location": "IN"
}
1 row in set (0.00 sec)
2.2 查找
可以在WHERE子句中使用col ->> path运算符来引用JSON的某一列
mysql> select emp_no, details
-> from employees.emp_details
-> where details ->> '$.address.pin' = "560103";
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| emp_no | details |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 1 | {"email": "abc@example.com", "phone": "+11800000000", "address": {"pin": "560103", "city": "Bangalore", "line1": "abc", "line2": "xyz street"}, "location": "IN"} |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
也可以使用JSON_CONTAINS函数查询数据。如果找到了数据，则返回1，否则返回0
mysql> select json_contains(details ->> '$.address.pin',"560103")
-> from employees.emp_details;
+-----------------------------------------------------+
| json_contains(details ->> '$.address.pin',"560103") |
+-----------------------------------------------------+
| 1 |
+-----------------------------------------------------+
1 row in set (0.00 sec)
如何查询一个key？使用JSON_CONTAINS_PATH函数检查address.line1是否存在
mysql> select json_contains_path(details, 'one', "$.address.line1")
-> from employees.emp_details;
+-------------------------------------------------------+
| json_contains_path(details, 'one', "$.address.line1") |
+-------------------------------------------------------+
| 1 |
+-------------------------------------------------------+
1 row in set (0.00 sec)
one表示至少应该存在一个键，检查address.line1或者address.line2是否存在
mysql> select json_contains_path(details, 'one', "$.address.line1", "$.address.line2")
-> from employees.emp_details;
+--------------------------------------------------------------------------+
| json_contains_path(details, 'one', "$.address.line1", "$.address.line2") |
+--------------------------------------------------------------------------+
| 1 |
+--------------------------------------------------------------------------+
1 row in set (0.00 sec)
如果要检查address.line1或者address.line5是否同时存在，可以使用all，而不是one
mysql> select json_contains_path(details, 'all', "$.address.line1", "$.address.line5")
-> from employees.emp_details;
+--------------------------------------------------------------------------+
| json_contains_path(details, 'all', "$.address.line1", "$.address.line5") |
+--------------------------------------------------------------------------+
| 0 |
+--------------------------------------------------------------------------+
1 row in set (0.00 sec)
2.3 修改
可以使用三种不同的函数来修改数据：JSON_SET()、JSON_INSERT()和JSON_REPLACE()。在MySQL 8之前的版本中，我们还需要对整个列进行完整的更新，这并不是最佳的方法。
2.3.1 JSON_SET()
替换现有值并添加不存在的值
mysql> update employees.emp_details
-> set details = json_set(details, "$.address.pin", "560100", "$.nickname","kai")
-> where emp_no = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select emp_no, json_pretty(details)
-> from employees.emp_details\G
*************************** 1. row ***************************
emp_no: 1
json_pretty(details): {
"email": "abc@example.com",
"phone": "+11800000000",
"address": {
"pin": "560100",
"city": "Bangalore",
"line1": "abc",
"line2": "xyz street"
},
"location": "IN",
"nickname": "kai"
}
1 row in set (0.00 sec)
2.3.2 JSON_INSERT()
插入值，但不替换现有值
在这种情况下，$.address.pin不会被更新，只会添加一个新的字段$.address.line4
mysql> update employees.emp_details
-> set details = json_insert(details, "$.address.pin", "560132", "$.address.line4","A Wing")
-> where emp_no = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select emp_no, json_pretty(details)
-> from employees.emp_details\G
*************************** 1. row ***************************
emp_no: 1
json_pretty(details): {
"email": "abc@example.com",
"phone": "+11800000000",
"address": {
"pin": "560100",
"city": "Bangalore",
"line1": "abc",
"line2": "xyz street",
"line4": "A Wing"
},
"location": "IN",
"nickname": "kai"
}
1 row in set (0.01 sec)
2.3.3 JSON_REPLACE()
仅替换现有值
在这种情况下，$.address.line5不会被添加，只有$.address.pin会被更新
mysql> update employees.emp_details
-> set details = json_replace(details, "$.address.pin", "560132", "$.address.line5","Landmark")
-> where emp_no = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select emp_no, json_pretty(details)
-> from employees.emp_details\G
*************************** 1. row ***************************
emp_no: 1
json_pretty(details): {
"email": "abc@example.com",
"phone": "+11800000000",
"address": {
"pin": "560132",
"city": "Bangalore",
"line1": "abc",
"line2": "xyz street",
"line4": "A Wing"
},
"location": "IN",
"nickname": "kai"
}
1 row in set (0.00 sec)
2.4 删除
JSON_REMOVE能从JSON文档中删除数据
mysql> update employees.emp_details
-> set details = json_remove(details, "$.address.line4")
-> where emp_no = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select emp_no, json_pretty(details)
-> from employees.emp_details\G
*************************** 1. row ***************************
emp_no: 1
json_pretty(details): {
"email": "abc@example.com",
"phone": "+11800000000",
"address": {
"pin": "560132",
"city": "Bangalore",
"line1": "abc",
"line2": "xyz street"
},
"location": "IN",
"nickname": "kai"
}
1 row in set (0.00 sec)
2.5 其他函数
JSON_KEYS()：获取JSON文档中的所有键
mysql> select json_keys(details),json_keys(details ->> "$.address")
-> from employees.emp_details
-> where emp_no= 1;
+-------------------------------------------------------+------------------------------------+
| json_keys(details) | json_keys(details ->> "$.address") |
+-------------------------------------------------------+------------------------------------+
| ["email", "phone", "address", "location", "nickname"] | ["pin", "city", "line1", "line2"] |
+-------------------------------------------------------+------------------------------------+
1 row in set (0.00 sec)
JSON_LENGTH()：给出JSON文档中的元素数
mysql> select json_length(details), json_length(details ->> "$.address")
-> from employees.emp_details
-> where emp_no= 1;
+----------------------+--------------------------------------+
| json_length(details) | json_length(details ->> "$.address") |
+----------------------+--------------------------------------+
| 5 | 4 |
+----------------------+--------------------------------------+
1 row in set (0.00 sec)
延伸阅读： https://dev.mysql.com/doc/refman/8.0/en/json-function-reference.html
参考文章
- MySQL进阶操作：JSON
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