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：
| NSERT 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"] 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) |
