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：

1234	CREATE TABLE json_test(id INT,person_desc TEXT)ENGINE INNODB;

我们来插入一条记录：

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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：

1	ALTER TABLE json_test MODIFY person_desc json;

先看看插入的这行JSON数据有哪些KEY：

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mysql> SELECT id,json_keys(person_desc) as "keys" FROM json_test\G*************************** 1. row *************************** id: 1keys: ["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：

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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：

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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。

1234	mysql> UPDATE json_test -> SET person_desc = json_remove(person_desc,'$.authors')\GQuery 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。

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mysql> SELECT json_contains_path(person_desc,'all','$.authors') as authors_exists FROM json_test\G*************************** 1. row ***************************authors_exists: 01 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。

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