MySQL5.7 JSON類型使用介紹

JSON是一種輕量級的數據交換格式，采用了獨立于語言的文本格式，類似XML，但是比XML簡單，易讀并且易編寫。對機器來說易于解析和生成，并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版本里面要實現這樣的存儲，要么用VARCHAR要么用TEXT大文本。 MySQL5.7發布后，專門設計了JSON數據類型以及關于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：

I

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，里面有三個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，然后在應用程序段來計算，畢竟數據庫是用來處理簡單數據的。