【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,'$.lastName') AS 'name', AUTHORS FROM
-> (
-> SELECT id,json_extract(person_desc,'$.authors') AS "authors" FROM json_test
-> UNION ALL
-> SELECT id,json_extract(person_desc,'$.authors') AS "authors" FROM json_test
-> UNION ALL
-> SELECT id,json_extract(person_desc,'$.authors') 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,'$.firstName') AS "firstname",
-> json_extract(AUTHORS,'$.lastName') AS "lastname",
-> json_extract(AUTHORS,'$.genre') AS "genre"
-> FROM
-> (
-> SELECT id,json_extract(person_desc,'$.authors') 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,'$.authors')\G
Query OK, 1 row affected (0.01 sec)
Rows matched: 1Changed: 1Warnings: 0 查找下对应的KEY，发现已经被删除掉了。
mysql> SELECT json_contains_path(person_desc,'all','$.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。
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