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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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"
}]
}'
);
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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"
]
1 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"
1 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
1 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。
本文转自 david_yeung 51CTO博客，原文链接：http://blog.51cto.com/yueliangdao0608/1711454，如需转载请自行联系原作者
