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：
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CREATE TABLE json_test( id INT, person_desc TEXT )ENGINE INNODB; |
我們來插入一條記錄：
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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：
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ALTER TABLE json_test MODIFY person_desc json; |
先看看插入的這行JSON數據有哪些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"] 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：
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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) |
現在來把詳細的值羅列出來：
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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" 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。
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mysql> UPDATE json_test -> SET person_desc = json_remove(person_desc,'$.authors')\G Query OK, 1 row affected (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 0 |
查找下對應的KEY，發現已經被刪除掉了。
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mysql> SELECT json_contains_path(person_desc,'all','$.authors') as authors_exist s FROM json_test\G *************************** 1. row *************************** authors_exists: 0 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。
總結
以上所述是小編給大家介紹的MySQL5.7 JSON類型使用詳解，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對服務器之家網站的支持！
原文鏈接：http://blog.csdn.net/yueliangdao0608/article/details/49760213
