MySQL 5.7 新特性之 JSON

從 MySQL 5.7.8 開始，MySQL 支持原生的 JSON 數據類型。

建立 JSON

相似 varchar，設置 JSON 主要將字段的 type 是 json, 不能設置長度，能夠是 NULL  但不能有默認值。

mysql> CREATE TABLE tb_json_test(
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `category` JSON,
    `tags` JSON,
    PRIMARY KEY (`id`)
);

mysql> DESC tb_json_test;
+----------+------------------+------+-----+---------+----------------+
| Field    | Type             | Null | Key | Default | Extra          |
+----------+------------------+------+-----+---------+----------------+
| id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| category | json             | YES  |     | NULL    |                |
| tags     | json             | YES  |     | NULL    |                |
+----------+------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

這樣 JSON 的字段就建立好了。

插入 JSON

就是插入 json 格式的字符串，能夠是對象的形式，也能夠是數組的形式

mysql> INSERT INTO `tb_json_test` (category, tags) VALUES ('{"id": 1, "name": "apple"}', '[1, 2, 3]');
Query OK, 1 row affected (0.01 sec)

MySQL 也有專門的函數 JSON_OBJECT，JSON_ARRAY 生成 json 格式的數據

mysql> INSERT INTO `tb_json_test` (category, tags) VALUES (JSON_OBJECT("id", 2, "name", "banana"), JSON_ARRAY(1, 3, 5));
Query OK, 1 row affected (0.00 sec)

查看插入的數據

mysql> SELECT * FROM tb_json_test;
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
|  2 | {"id": 2, "name": "banana"}  | [1, 3, 5] |
+----+------------------------------+-----------+
2 rows in set (0.00 sec)

更多生成 JSON 值的函數請參考： http://dev.mysql.com/doc/refman/5.7/en/json-creation-functions.html

查詢 JSON

查詢 json 中的數據用 column->path 的形式，其中對象類型 path 這樣表示 $.path, 而數組類型則是 $[index]

mysql> SELECT id, category->'$.id', category->'$.name', tags->'$[0]', tags->'$[2]' FROM tb_json_test;
+----+------------------+--------------------+--------------+--------------+
| id | category->'$.id' | category->'$.name' | tags->'$[0]' | tags->'$[2]' |
+----+------------------+--------------------+--------------+--------------+
|  1 | 1                | "apple"            | 1            | 3            |
|  2 | 2                | "banana"           | 1            | 5            |
+----+------------------+--------------------+--------------+--------------+
2 rows in set (0.00 sec)

能夠看到對應字符串類型的 category->'$.name' 中還包含着雙引號，這其實並非想要的結果，能夠用 JSON_UNQUOTE 函數將雙引號去掉，從 MySQL 5.7.13 起也能夠經過這個操做符 ->> 這個和 JSON_UNQUOTE 是等價的

mysql> SELECT id, category->'$.name', JSON_UNQUOTE(category->'$.name'), category->>'$.name' FROM tb_json_test;
+----+--------------------+----------------------------------+---------------------+
| id | category->'$.name' | JSON_UNQUOTE(category->'$.name') | category->>'$.name' |
+----+--------------------+----------------------------------+---------------------+
|  1 | "apple"            | apple                            | apple               |
|  2 | "banana"           | banana                           | banana              |
+----+--------------------+----------------------------------+---------------------+
2 rows in set (0.00 sec)

下面說下 JSON 做爲條件進行搜索。由於 JSON 不一樣於字符串，因此若是用字符串和 JSON 字段比較，是不會相等的

mysql> SELECT * FROM tb_json_test WHERE category = '{"id": 1, "name": "apple"}';
Empty set (0.00 sec)

這時能夠經過 CAST 將字符串轉成 JSON 的形式

mysql> SELECT * FROM tb_json_test WHERE category = CAST('{"id": 1, "name": "lnmp.cn"}' as JSON);
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "lnmp.cn"} | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.00 sec)

經過 JSON 中的元素進行查詢, 對象型的查詢一樣能夠經過 column->path

mysql> SELECT * FROM tb_json_test WHERE category->'$.name' = 'apple';
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.00 sec)

上面有提到 column->path 形式從 select 中查詢出來的字符串是包含雙引號的，但做爲條件這裏其實沒什麼影響，-> 和 ->> 結果是同樣的

mysql> SELECT * FROM tb_json_test WHERE category->>'$.name' = 'apple';
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.00 sec)

要特別注意的是，JSON 中的元素搜索是嚴格區分變量類型的，好比說整型和字符串是嚴格區分的

mysql> SELECT * FROM tb_json_test WHERE category->'$.id' = '1';
Empty set (0.00 sec)

mysql> SELECT * FROM tb_json_test WHERE category->'$.id' = 1;
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.00 sec)

能夠看到搜索字符串 1 和整型 1 的結果是不同的。

除了用 column->path 的形式搜索，還能夠用JSON_CONTAINS 函數，但和 column->path 的形式有點相反的是，JSON_CONTAINS 第二個參數是不接受整數的，不管 json 元素是整型仍是字符串，不然會出現這個錯誤

mysql> SELECT * FROM tb_json_test WHERE JSON_CONTAINS(category, 1, '$.id');
ERROR 3146 (22032): Invalid data type for JSON data in argument 2 to function json_contains; a JSON string or JSON type is required.

這裏必須是要字符串 1

mysql> SELECT * FROM tb_json_test WHERE JSON_CONTAINS(category, '1', '$.id');
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.01 sec)

對於數組類型的 JSON 的查詢，好比說 tags 中包含有 2 的數據，一樣要用 JSON_CONTAINS 函數，一樣第二個參數也須要是字符串

mysql> SELECT * FROM tb_json_test WHERE JSON_CONTAINS(tags, '2');
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 2, 3] |
+----+------------------------------+-----------+
1 row in set (0.00 sec)

更多搜索 JSON 值的函數請參考：http://dev.mysql.com/doc/refman/5.7/en/json-search-functions.html

更新 JSON

若是是整個 json 更新的話，和插入時相似的。

mysql> UPDATE tb_json_test SET tags = '[1, 3, 4]' WHERE id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM tb_json_test ;
+----+------------------------------+-----------+ 
| id | category                     | tags      | 
+----+------------------------------+-----------+ 
| 1  | {"id": 1, "name": "apple"}   | [1, 3, 4] | 
| 2  | {"id": 2, "name": "banana"}  | [1, 3, 5] |
+----+------------------------------+-----------+
2 rows in set (0.00 sec)

但若是要更新 JSON 下的元素，MySQL 並不支持 column->path 的形式

mysql> UPDATE lnmp SET category->'$.name' = 'pear', tags->'$[0]' = 2 WHERE id = 1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '->'$.name' = 'pear', tags->'$[0]' = 2 WHERE id = 1' at line 1

則可能要用到如下幾個函數

JSON_INSERT() 插入新值，但不會覆蓋已經存在的值

mysql> UPDATE lnmp SET category = JSON_INSERT(category, '$.name', 'pear', '$.weight', '100') WHERE id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM tb_json_test;
+----+----------------------------------------------------+-----------+
| id | category                                           | tags      |
+----+----------------------------------------------------+-----------+
|  1 | {"id": 1, "weight": "100", "name": "apple"}        | [1, 3, 4] |
|  2 | {"id": 2, "name": "banana"}                        | [1, 3, 5] |
+----+----------------------------------------------------+-----------+
2 rows in set (0.00 sec)

能夠看到 name 沒有被修改，但新元素 weight 已經添加進去

JSON_SET() 插入新值，並覆蓋已經存在的值

mysql> UPDATE tb_json_test SET category = JSON_SET(category, '$.color', 'yellow', '$.weight', '200') WHERE id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM tb_json_test;
+----+----------------------------------------------------------------------------------+-----------+
| id | category                                                                         | tags      |
+----+----------------------------------------------------------------------------------+-----------+
|  1 | {"id": 1, "weight": "200", "color": "yellow", "name": "apple"}                   | [1, 3, 4] |
|  2 | {"id": 2, "name": "banana"}                                                      | [1, 3, 5] |
+----+----------------------------------------------------------------------------------+-----------+
2 rows in set (0.00 sec)

能夠看到 color已經插入，weight已經被修改

JSON_REPLACE() 只替換存在的值

mysql> UPDATE tb_json_test SET category = JSON_REPLACE(category, '$.name', 'orange', '$.weight', '150') WHERE id = 2;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM lnmp;
+----+----------------------------------------------------------------------------------+-----------+
| id | category                                                                         | tags      |
+----+----------------------------------------------------------------------------------+-----------+
|  1 | {"id": 1, "url": "http://www.lnmp.cn", "host": "www.lnmp.cn", "name": "lnmp.cn"} | [1, 3, 4] |
|  2 | {"id": 2, "name": "orange"}                                                         | [1, 3, 5] |
+----+----------------------------------------------------------------------------------+-----------+
2 rows in set (0.00 sec)

能夠看到 name 已經被替換，weight 不存在被忽略。

JSON_REMOVE() 刪除 JSON 元素

mysql> UPDATE tb_json_test SET category = JSON_REMOVE(category, '$.weight', '$.color') WHERE id = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM lnmp;
+----+------------------------------+-----------+
| id | category                     | tags      |
+----+------------------------------+-----------+
|  1 | {"id": 1, "name": "apple"}   | [1, 3, 4] |
|  2 | {"id": 2, "name": "banana"}  | [1, 3, 5] |
+----+------------------------------+-----------+
2 rows in set (0.00 sec)

更多函數請參考：http://dev.mysql.com/doc/refman/5.7/en/json-modification-functions.html