【原创】MySQL5.7 JSON类型使用介绍_PHP教程
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2022-06-14 14:52:05
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【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,'$.lastName[0]') AS 'name', AUTHORS FROM
- -> (
- -> SELECT id,json_extract(person_desc,'$.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。
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