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:
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CREATE TABLE json_test(
id INT ,
person_desc TEXT
)ENGINE INNODB;
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我们来插入一条记录:
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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"
}]
}' );
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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:
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ALTER TABLE json_test MODIFY person_desc json;
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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: 1
keys: [ "authors" , "musicians" , "programmers" ]
row in set (0.00 sec)
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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)
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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"
row in set (0.00 sec)
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我们进一步来演示把authors 这个KEY对应的所有对象删掉。
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mysql> UPDATE json_test
-> SET person_desc = json_remove(person_desc, '$.authors' )\G
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
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查找下对应的KEY,发现已经被删除掉了。
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mysql> SELECT json_contains_path(person_desc, 'all' , '$.authors' ) as authors_exist
s FROM json_test\G
*************************** 1. row ***************************
authors_exists: 0
row in set (0.00 sec)
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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。
总结
以上所述是小编给大家介绍的MySQL5.7 JSON类型使用详解,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对服务器之家网站的支持!
原文链接:http://blog.csdn.net/yueliangdao0608/article/details/49760213