MySQL5.7 JSON类型使用详解

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) 

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" 
 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 
 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。

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网站的支持!

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