【原創】MySQL5.7 JSON類型使用介紹

【原創】MySQL5.7 JSON類型使用介紹

JSON是一種輕量級的數據交換格式，采用了獨立於語言的文本格式，類似XML，但是比XML簡單，易讀並且易編寫。對機器來說易於解析和生成，並且會減少網絡帶寬的傳輸。
JSON的格式非常簡單：名稱/鍵值。之前MySQL版本裡面要實現這樣的存儲，要麼用VARCHAR要麼用TEXT大文本。 MySQL5.7發布後，專門設計了JSON數據類型以及關於這種類型的檢索以及其他函數解析。 我們先看看MySQL老版本的JSON存取。


示例表結構：

CREATE TABLE json_test(
id INT,
person_desc TEXT
)ENGINE INNODB;

我們來插入一條記錄：

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"
}]
}');

那一般我們遇到這樣來存儲JSON格式的話，只能把這條記錄取出來交個應用程序，有應用程序來解析。


現在到了MySQL5.7，我們重新修改下表結構：

ALTER TABLE json_test MODIFY person_desc json;

先看看插入的這行JSON數據有哪些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)

我們可以看到，裡面有三個KEY，分別為authors，musicians，programmers。那現在找一個KEY把對應的值拿出來：

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)

現在來把詳細的值羅列出來：

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)

我們進一步來演示把authors 這個KEY對應的所有對象刪掉。

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

查找下對應的KEY，發現已經被刪除掉了。

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)

總結下， 雖然MySQL5.7 開始支持JSON數據類型，但是我建議如果要使用的話，最好是把這樣的值取出來，然後在應用程序段來計算，畢竟數據庫是用來處理簡單數據的。