【原创】MySQL5.7 JSON类型使用介绍

程序员文章站 2022-04-27 12:32:18

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【原创】MySQL5.7 JSON类型使用介绍

JSON是一种轻量级的数据交换格式，采用了独立于语言的文本格式，类似XML，但是比XML简单，易读并且易编写。对机器来说易于解析和生成，并且会减少网络带宽的传输。
JSON的格式非常简单：名称/键值。之前MySQL版本里面要实现这样的存储，要么用VARCHAR要么用TEXT大文本。 MySQL5.7发布后，专门设计了JSON数据类型以及关于这种类型的检索以及其他函数解析。我们先看看MySQL老版本的JSON存取。

示例表结构：


CREATE TABLE json_test(


id INT,


person_desc TEXT


)ENGINE INNODB;

我们来插入一条记录：


INSERT INTO json_test VALUES (1,'{


"programmers": [{


"firstName": "Brett",


"lastName": "McLaughlin",


"email": "aaaa"


}, {


"firstName": "Jason",


"lastName": "Hunter",


"email": "bbbb"


}, {


"firstName": "Elliotte",


"lastName": "Harold",


"email": "cccc"


}],


"authors": [{


"firstName": "Isaac",


"lastName": "Asimov",


"genre": "sciencefiction"


}, {


"firstName": "Tad",


"lastName": "Williams",


"genre": "fantasy"


}, {


"firstName": "Frank",


"lastName": "Peretti",


"genre": "christianfiction"


}],


"musicians": [{


"firstName": "Eric",


"lastName": "Clapton",


"instrument": "guitar"


}, {


"firstName": "Sergei",


"lastName": "Rachmaninoff",


"instrument": "piano"


}]


}');

那一般我们遇到这样来存储JSON格式的话，只能把这条记录取出来交个应用程序，有应用程序来解析。

现在到了MySQL5.7，我们重新修改下表结构：

ALTER TABLE json_test MODIFY person_desc json;

先看看插入的这行JSON数据有哪些KEY：


mysql> SELECT id,json_keys(person_desc) as "keys" FROM json_test\G


*************************** 1. row ***************************


id: 1


keys: ["authors", "musicians", "programmers"]


1 row in set (0.00 sec)

我们可以看到，里面有三个KEY，分别为authors，musicians，programmers。那现在找一个KEY把对应的值拿出来：


mysql> SELECT json_extract(AUTHORS,'$.lastName[0]') AS 'name', AUTHORS FROM


-> (


-> SELECT id,json_extract(person_desc,'$.authors[0][0]') AS "authors" FROM json_test


-> UNION ALL


-> SELECT id,json_extract(person_desc,'$.authors[1][0]') AS "authors" FROM json_test


-> UNION ALL


-> SELECT id,json_extract(person_desc,'$.authors[2][0]') AS "authors" FROM json_test


-> ) AS T1


-> ORDER BY NAME DESC\G


*************************** 1. row ***************************


name: "Williams"


AUTHORS: {"genre": "fantasy", "lastName": "Williams", "firstName": "Tad"}


*************************** 2. row ***************************


name: "Peretti"


AUTHORS: {"genre": "christianfiction", "lastName": "Peretti", "firstName": "Frank"}


*************************** 3. row ***************************


name: "Asimov"


AUTHORS: {"genre": "sciencefiction", "lastName": "Asimov", "firstName": "Isaac"}






3 rows in set (0.00 sec)

现在来把详细的值罗列出来：


mysql> SELECT


-> json_extract(AUTHORS,'$.firstName[0]') AS "firstname",


-> json_extract(AUTHORS,'$.lastName[0]') AS "lastname",


-> json_extract(AUTHORS,'$.genre[0]') AS "genre"


-> FROM


-> (


-> SELECT id,json_extract(person_desc,'$.authors[0]') AS "authors" FROM json


_test


-> ) AS T\G


*************************** 1. row ***************************


firstname: "Isaac"


lastname: "Asimov"


genre: "sciencefiction"


1 row in set (0.00 sec)

我们进一步来演示把authors 这个KEY对应的所有对象删掉。


mysql> UPDATE json_test


-> SET person_desc = json_remove(person_desc,'$.authors')\G


Query OK, 1 row affected (0.01 sec)


Rows matched: 1  Changed: 1  Warnings: 0

查找下对应的KEY，发现已经被删除掉了。


mysql> SELECT json_contains_path(person_desc,'all','$.authors') as authors_exist


s FROM json_test\G


*************************** 1. row ***************************


authors_exists: 0


1 row in set (0.00 sec)

总结下，虽然MySQL5.7 开始支持JSON数据类型，但是我建议如果要使用的话，最好是把这样的值取出来，然后在应用程序段来计算，毕竟数据库是用来处理简单数据的。

【原创】MySQL5.7 JSON类型使用介绍