MySQL5.7 JSON型別使用介紹

航空母艦發表於2017-01-13
MySqlJSON型別

JSON是一種輕量級的資料交換格式，採用了獨立於語言的文字格式，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，並且會減少網路頻寬的傳輸。
    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儲存，要麼用VARCHAR要麼用TEXT大文字。 MySQL5.7釋出後，專門設計了JSON資料型別以及關於這種型別的檢索以及其他函式解析。 我們先看看MySQL老版本的JSON存取。

CREATE TABLE `json_test` (
  `id` int(11) DEFAULT NULL,
  `person_desc` text
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

 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儲存JSON格式的話，只能把這條記錄取出來交個應用程式，有應用程式來解析.

 

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資料有哪些KEY：

SELECT id,json_keys(person_desc) as "keys" FROM json_test

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對應的所有物件刪掉。

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

 查詢下對應的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 開始支援JSON資料型別，但是我建議如果要使用的話，最好是把這樣的值取出來，然後在應用程式段來計算，畢竟資料庫是用來處理簡單資料的。

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