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_testG
*************************** 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 DESCG
*************************** 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 TG
*************************** 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_testG
*************************** 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。