JSON是一種輕量級的數(shù)據(jù)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(wǎng)絡(luò)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(xiàn)這樣的存儲，要么用VARCHAR要么用TEXT大文本。 MySQL5.7發(fā)布后，專門設(shè)計了JSON數(shù)據(jù)類型以及關(guān)于這種類型的檢索以及其他函數(shù)解析。 我們先看看MySQL老版本的JSON存取。
示例表結(jié)構(gòu)：
| CREATE TABLE json_test( id INT, person_desc TEXT )ENGINE INNODB; |
我們來插入一條記錄：
| 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(yīng)用程序，有應(yīng)用程序來解析。
現(xiàn)在到了MySQL5.7，我們重新修改下表結(jié)構(gòu)：
| ALTER TABLE json_test MODIFY person_desc json; |
先看看插入的這行JSON數(shù)據(jù)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"] 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(xiàn)在找一個KEY把對應(yīng)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) |
