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：

I

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"]  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。