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MySQL - MySQL 8.0進階操作：JSON

本文轉載自   查看原文   2020-04-13 17:53   1845 

轉載 最后發布於2019-08-08 20:23:56 閱讀數 1402  收藏

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 此學習文是基於MySQL 8.0寫的
得益於大神朋友的悉心指導解決不少坑，才寫出此文，向大神奉上膝蓋

  要在MySQL中存儲數據，就必須定義數據庫和表結構(schema)，這是一個主要的限制。為了應對這一點，從MySQL 5.7開始，MySQL支恃了 JavaScript對象表示(JavaScriptObject Notation，JSON) 數據類型。之前，這類數據不是單獨的數據類型，會被存儲為字符串。新的JSON數據類型提供了自動驗證的JSON文檔以及優化的存儲格式。

JSON文檔以二進制格式存儲，它提供以下功能：

對文檔元素的快速讀取訪問。
當服務器再次讀取JSON文檔時，不需要重新解析文本獲取該值。
通過鍵或數組索引直接查找子對象或嵌套值，而不需要讀取文檔中的所有值。
創建一個測試表

  1.  
    mysql> create table employees.emp_details (
  2.  
        -> emp_no int primary key,
  3.  
        -> details json
  4.  
        -> );
  5.  
    Query OK, 0 rows affected (0.17 sec)
  6.  
     
  7.  
    mysql> desc employees.emp_details;
  8.  
    +---------+---------+------+-----+---------+-------+
  9.  
    | Field   | Type    | Null | Key | Default | Extra |
  10.  
    +---------+---------+------+-----+---------+-------+
  11.  
    | emp_no  | int( 11) | NO   | PRI | NULL    |       |
  12.  
    | details | json    | YES  |     | NULL    |       |
  13.  
    +---------+---------+------+-----+---------+-------+
  14.  
    2 rows in set (0.00 sec)

 插入JSON

  1.  
    mysql> insert into employees.emp_details (emp_no, details)
  2.  
        -> values (' 1',
  3.  
        -> '{ "location":"IN","phone":"+11800000000","email":"abc@example.com","address":{"line1":"abc","line2":"xyz street","city":"Bangalore","pin":"560103"}}'
  4.  
        -> );
  5.  
    Query OK, 1 row affected (0.13 sec)
  6.  
     
  7.  
    mysql> select emp_no, details from employees.emp_details;
  8.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  9.  
    | emp_no | details                                                                                                                                                           |
  10.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  11.  
    |       1 | {"email": "abc@example.com", "phone": "+11800000000", "address": {"pin": "560103", "city": "Bangalore", "line1": "abc", "line2": "xyz street"}, "location": "IN"} |
  12.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  13.  
    1 row in set (0.00 sec)

檢索JSON
可以使用->和->>運算符檢索JSON列的字段：

  1.  
    mysql> select emp_no, details -> '$.address.pin' pin 
  2.  
        -> from employees.emp_details;
  3.  
    +--------+----------+
  4.  
    | emp_no | pin      |
  5.  
    +--------+----------+
  6.  
    |       1 | "560103" |
  7.  
    +--------+----------+
  8.  
    1 row in set (0.00 sec)

如果不用引號檢索數據，可以使用->> 運算符（推薦此方式）

  1.  
    mysql> select emp_no, details ->> '$.address.pin' pin 
  2.  
        -> from employees.emp_details;
  3.  
    +--------+--------+
  4.  
    | emp_no | pin    |
  5.  
    +--------+--------+
  6.  
    |       1 | 560103 |
  7.  
    +--------+--------+
  8.  
    1 row in set (0.00 sec)

JSON函數
MySQL提供了許多處理JSON數據的函數，讓我們看看最常用的幾種函數。

1. 優雅瀏覽
想要以優雅的格式顯示JSON值，請使用JSON_PRETTY()函數

  1.  
    mysql> select emp_no, json_pretty(details) 
  2.  
        -> from employees.emp_details\ G
  3.  
    *************************** 1. row ***************************
  4.  
                  emp_no: 1
  5.  
    json_pretty(details): {
  6.  
      "email": "abc@example.com",
  7.  
      "phone": "+11800000000",
  8.  
      "address": {
  9.  
        "pin": "560103",
  10.  
        "city": "Bangalore",
  11.  
        "line1": "abc",
  12.  
        "line2": "xyz street"
  13.  
      },
  14.  
      "location": "IN"
  15.  
    }
  16.  
    1 row in set (0.00 sec)

2. 查找
可以在WHERE子句中使用col ->> path運算符來引用JSON的某一列

  1.  
    mysql> select emp_no, details 
  2.  
        -> from employees.emp_details 
  3.  
        -> where details ->> '$.address.pin' = "560103";
  4.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  5.  
    | emp_no | details                                                                                                                                                           |
  6.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  7.  
    |       1 | {"email": "abc@example.com", "phone": "+11800000000", "address": {"pin": "560103", "city": "Bangalore", "line1": "abc", "line2": "xyz street"}, "location": "IN"} |
  8.  
    +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  9.  
    1 row in set (0.00 sec)

也可以使用JSON_CONTAINS函數查詢數據。如果找到了數據，則返回1，否則返回0

  1.  
    mysql> select json_contains(details ->> '$.address.pin', "560103") 
  2.  
        -> from employees.emp_details;
  3.  
    +-----------------------------------------------------+
  4.  
    | json_contains(details ->> '$.address.pin', "560103") |
  5.  
    +-----------------------------------------------------+
  6.  
    |                                                   1 |
  7.  
    +-----------------------------------------------------+
  8.  
    1 row in set (0.00 sec)

如何查詢一個key？使用JSON_CONTAINS_PATH函數檢查address. line1是否存在

  1.  
    mysql> select json_contains_path(details, 'one', "$.address.line1") 
  2.  
        -> from employees.emp_details;
  3.  
    +-------------------------------------------------------+
  4.  
    | json_contains_path(details, 'one', "$.address.line1") |
  5.  
    +-------------------------------------------------------+
  6.  
    |                                                     1 |
  7.  
    +-------------------------------------------------------+
  8.  
    1 row in set (0.00 sec)

one表示至少應該存在一個鍵，檢查address.line1或者address.line2是否存在

  1.  
    mysql> select json_contains_path(details, 'one', "$.address.line1", "$.address.line2") 
  2.  
        -> from employees.emp_details;
  3.  
    +--------------------------------------------------------------------------+
  4.  
    | json_contains_path(details, 'one', "$.address.line1", "$.address.line2") |
  5.  
    +--------------------------------------------------------------------------+
  6.  
    |                                                                         1 |
  7.  
    +--------------------------------------------------------------------------+
  8.  
    1 row in set (0.00 sec)

如果要檢查address.line1或者address.line5是否同時存在，可以使用all，而不是one

  1.  
    mysql> select json_contains_path(details, 'all', "$.address.line1", "$.address.line5") 
  2.  
        -> from employees.emp_details;
  3.  
    +--------------------------------------------------------------------------+
  4.  
    | json_contains_path(details, 'all', "$.address.line1", "$.address.line5") |
  5.  
    +--------------------------------------------------------------------------+
  6.  
    |                                                                         0 |
  7.  
    +--------------------------------------------------------------------------+
  8.  
    1 row in set (0.00 sec)

3. 修改

可以使用三種不同的函數來修改數據：JSON_SET()、JSON_INSERT()和JSON _REPLACE()。 在MySQL 8之前的版本中，我們還需要對整個列進行完整的更新，這並不是最佳的方法。

3.1. JSON_SET() 替換現有值並添加不存在的值

  1.  
    mysql> update employees.emp_details 
  2.  
        -> set details = json_set(details, "$.address.pin", "560100", "$.nickname","kai") 
  3.  
        -> where emp_no = 1;
  4.  
    Query OK, 1 row affected (0.01 sec)
  5.  
    Rows matched: 1  Changed: 1  Warnings: 0
  6.  
     
  7.  
    mysql> select emp_no, json_pretty(details) 
  8.  
        -> from employees.emp_details\ G
  9.  
    *************************** 1. row ***************************
  10.  
                  emp_no: 1
  11.  
    json_pretty(details): {
  12.  
      "email": "abc@example.com",
  13.  
      "phone": "+11800000000",
  14.  
      "address": {
  15.  
        "pin": "560100",
  16.  
        "city": "Bangalore",
  17.  
        "line1": "abc",
  18.  
        "line2": "xyz street"
  19.  
      },
  20.  
      "location": "IN",
  21.  
      "nickname": "kai"
  22.  
    }
  23.  
    1 row in set (0.00 sec)

3.2. JSON_INSERT() 插入值，但不替換現有值
在這種情況下，$.address.pin不會被更新，只會添加一個新的字段$.address.line4

  1.  
    mysql> update employees.emp_details 
  2.  
        -> set details = json_insert(details, "$.address.pin", "560132", "$.address.line4","A Wing") 
  3.  
        -> where emp_no = 1;
  4.  
    Query OK, 1 row affected (0.01 sec)
  5.  
    Rows matched: 1  Changed: 1  Warnings: 0
  6.  
     
  7.  
    mysql> select emp_no, json_pretty(details) 
  8.  
        -> from employees.emp_details\ G
  9.  
    *************************** 1. row ***************************
  10.  
                  emp_no: 1
  11.  
    json_pretty(details): {
  12.  
      "email": "abc@example.com",
  13.  
      "phone": "+11800000000",
  14.  
      "address": {
  15.  
        "pin": "560100",
  16.  
        "city": "Bangalore",
  17.  
        "line1": "abc",
  18.  
        "line2": "xyz street",
  19.  
        "line4": "A Wing"
  20.  
      },
  21.  
      "location": "IN",
  22.  
      "nickname": "kai"
  23.  
    }
  24.  
    1 row in set (0.01 sec)

3.3. JSON_REPLACE()
僅替換現有值
在這種情況下，$.address.line5不會被添加， 只有$.address.pin會被更新

  1.  
    mysql> update employees.emp_details 
  2.  
        -> set details = json_replace(details, "$.address.pin", "560132", "$.address.line5","Landmark") 
  3.  
        -> where emp_no = 1;
  4.  
    Query OK, 1 row affected (0.00 sec)
  5.  
    Rows matched: 1  Changed: 1  Warnings: 0
  6.  
     
  7.  
    mysql> select emp_no, json_pretty(details) 
  8.  
        -> from employees.emp_details\ G
  9.  
    *************************** 1. row ***************************
  10.  
                  emp_no: 1
  11.  
    json_pretty(details): {
  12.  
      "email": "abc@example.com",
  13.  
      "phone": "+11800000000",
  14.  
      "address": {
  15.  
        "pin": "560132",
  16.  
        "city": "Bangalore",
  17.  
        "line1": "abc",
  18.  
        "line2": "xyz street",
  19.  
        "line4": "A Wing"
  20.  
      },
  21.  
      "location": "IN",
  22.  
      "nickname": "kai"
  23.  
    }
  24.  
    1 row in set (0.00 sec)

4. 刪除 JSON_REMOVE能從JSON文檔中刪除數據

  1.  
    mysql> update employees.emp_details 
  2.  
        -> set details = json_remove(details, "$.address.line4") 
  3.  
        -> where emp_no = 1;
  4.  
    Query OK, 1 row affected (0.01 sec)
  5.  
    Rows matched: 1  Changed: 1  Warnings: 0
  6.  
     
  7.  
    mysql> select emp_no, json_pretty(details) 
  8.  
        -> from employees.emp_details\ G
  9.  
    *************************** 1. row ***************************
  10.  
                  emp_no: 1
  11.  
    json_pretty(details): {
  12.  
      "email": "abc@example.com",
  13.  
      "phone": "+11800000000",
  14.  
      "address": {
  15.  
        "pin": "560132",
  16.  
        "city": "Bangalore",
  17.  
        "line1": "abc",
  18.  
        "line2": "xyz street"
  19.  
      },
  20.  
      "location": "IN",
  21.  
      "nickname": "kai"
  22.  
    }
  23.  
    1 row in set (0.00 sec)

5. 其他函數

 JSON_KEYS()：獲取JSON文檔中的所有鍵

  1.  
    mysql> select json_keys(details),json_keys(details ->> "$.address") 
  2.  
        -> from employees.emp_details 
  3.  
        -> where emp_no= 1;
  4.  
    +-------------------------------------------------------+------------------------------------+
  5.  
    | json_keys(details)                                    | json_keys(details ->> "$.address") |
  6.  
    +-------------------------------------------------------+------------------------------------+
  7.  
    | [ "email", "phone", "address", "location", "nickname"] | ["pin", "city", "line1", "line2"]  |
  8.  
    +-------------------------------------------------------+------------------------------------+
  9.  
    1 row in set (0.00 sec)

JSON_LENGTH()：給出JSON文檔中的元素數
 

  1.  
    mysql> select json_length(details), json_length(details ->> "$.address") 
  2.  
        -> from employees.emp_details 
  3.  
        -> where emp_no= 1;
  4.  
    +----------------------+--------------------------------------+
  5.  
    | json_length(details) | json_length(details ->> "$.address") |
  6.  
    +----------------------+--------------------------------------+
  7.  
    |                     5 |                                    4 |
  8.  
    +----------------------+--------------------------------------+
  9.  
    1 row in set (0.00 sec)

延伸閱讀： https://dev.mysql.com/doc/refman/8.0/en/json-function-reference.html 


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