mysql5.7 version begins to support JSON type fields2. Create Example tablejson_extract can be completely abbreviated as
-> json_unquote(json_extract()) can be completely abbreviated as
->>Most of the following introductions will use the abbreviation
CREATE TABLE `test_json` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`content` json DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4;
# 插入两条测试用的记录
INSERT INTO `test_json` (`content`) VALUES ('{\"name\":\"tom\",\"age\":18,\"score\":[100,90,87],\"address\":{\"province\":\"湖南\",\"city\":\"长沙\"}}');
INSERT INTO `test_json` (`content`) VALUES ('[1, "apple", "red", {"age": 18, "name": "tom"}]');
content | |
---|---|
{"age": 18, "name": "tom", "score": [100, 90, 87], "address": {"city": "Changsha", "province": "Hunan"}} | |
[1, “apple”, “red”, {“age”: 18, “name”: “tom”}] |
- In the json_extract function, the first One parameter content represents json data, and the second parameter is the json path, where $ represents the json data itself, and $.name represents obtaining the value with the key name in json
- You can use -> expression instead of json_extract
- If the obtained val itself is a string, then the obtained val will be wrapped in quotation marks, such as "tom", this kind of data is When parsed into a program object, it may be escaped as \"tom\". In order to solve this problem, you can wrap another layer of json_unquote function outside, or use ->> instead of ->
content:- Get an element in the JSON array{" age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “Changsha”, “province”: “Hunan”}}
# 得到"tom" select json_extract(content,'$.name') from test_json where id = 1; # 简写方式:字段名->表达式等价于json_extract(字段名,表达式) select content->'$.name' from test_json where id = 1; # 结果: +--------------------------------+ | json_extract(content,'$.name') | +--------------------------------+ | "tom" | +--------------------------------+ +-------------------+ | content->'$.name' | +-------------------+ | "tom" | +-------------------+ # 解除双引号,得到tom select json_unquote(json_extract(content,'$.name')) from test_json where id = 1; # 简写方式:字段名->>表达式等价于json_unquote(json_extract(字段名,表达式)) select content->>'$.name' from test_json where id = 1; # 结果: +----------------------------------------------+ | json_unquote(json_extract(content,'$.name')) | +----------------------------------------------+ | tom | +----------------------------------------------+ +--------------------+ | content->>'$.name' | +--------------------+ | tom | +--------------------+
- In the json_extract function, the first parameter content represents json data, and the second parameter is the json path, where $ Represents the json data itself, $[i] indicates obtaining the element with index i of the json array (the index starts from 0)
- is the same as obtaining key-val, if the obtained element is For strings, the default method will also get characters enclosed in double quotes, causing the program to escape. The method is also to use the json_unquote function, or use ->> instead of ->
[1, “apple”, “red”, {“age”: 18, “name”: “tom”}]
# 得到"apple" select json_extract(content,'$[1]') from test_json where id = 2; # 简写,效果同上 select content->'$[1]' from test_json where id = 2; # 结果: +------------------------------+ | json_extract(content,'$[1]') | +------------------------------+ | "apple" | +------------------------------+ +-----------------+ | content->'$[1]' | +-----------------+ | "apple" | +-----------------+ # 解除双引号,得到apple select json_unquote(json_extract(content,'$[1]')) from test_json where id = 2; # 简写,效果同上 select content->>'$[1]' from test_json where id = 2; # 结果: +--------------------------------------------+ | json_unquote(json_extract(content,'$[1]')) | +--------------------------------------------+ | apple | +--------------------------------------------+ +------------------+ | content->>'$[1]' | +------------------+ | apple | +------------------+- Get JSON Nested data
Combined with the two acquisition methods introduced earlier, you can obtain the nested data in json data
content: id=1{"age": 18 , “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “Changsha”, “province”: “Hunan”}}content: id= 2
[1, “apple”, “red”, {“age”: 18, “name”: “tom”}]# 得到:87 select content->'$.score[2]' from test_json where id = 1; # 结果: +-----------------------+ | content->'$.score[2]' | +-----------------------+ | 87 | +-----------------------+ # 得到:18 select content->'$[3].age' from test_json where id = 2; # 结果: +---------------------+ | content->'$[3].age' | +---------------------+ | 18 | +---------------------+4. Getting better
- Obtain JSON data of multiple paths
Will combine the data of multiple paths into an array and return
content: id=1{"age": 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “Changsha”, “province”: “Hunan”}}
select json_extract(content,'$.age','$.score') from test_json where id = 1; # 结果: +-----------------------------------------+ | json_extract(content,'$.age','$.score') | +-----------------------------------------+ | [18, [100, 90, 87]] | +-----------------------------------------+ select json_extract(content,'$.name','$.address.province','$.address.city') from test_json where id = 1; # 结果: +----------------------------------------------------------------------+ | json_extract(content,'$.name','$.address.province','$.address.city') | +----------------------------------------------------------------------+ | ["tom", "湖南", "长沙"] | +----------------------------------------------------------------------+- The use of path expression *
will combine the data of multiple paths into an array and return
# 先插入一条用于测试的数据 INSERT INTO `test_json` (`id`,`content`) VALUES(3,'{"name":"tom","address":{"name":"中央公园","city":"长沙"},"class":{"id":3,"name":"一年三班"},"friend":[{"age":20,"name":"marry"},{"age":21,"name":"Bob"}]}')content: id=3
{“name ": "tom", "class": {"id": 3, "name": "Class Three a Year"}, "friend": [{"age": 20, "name": "marry"}, {"age": 21, "name": "Bob"}], "address": {"city": "Changsha", "name": "Central Park"}}content: id=1
# 获取所有二级嵌套中key=name的值 # 由于friend的二级嵌套是一个数组,所以.name获取不到其中的所有name值 select content->'$.*.name' from test_json where id = 3; +----------------------------------+ | content->'$.*.name' | +----------------------------------+ | ["一年三班", "中央公园"] | +----------------------------------+``` # 获取所有key为name值的数据,包括任何嵌套内的name select content->'$**.name' from test_json where id = 3; +---------------------------------------------------------+ | content->'$**.name' | +---------------------------------------------------------+ | ["tom", "一年三班", "marry", "Bob", "中央公园"] | +---------------------------------------------------------+ # 获取数组中所有的name值 select content->'$.friend[*].name' from test_json where id = 3; +-----------------------------+ | content->'$.friend[*].name' | +-----------------------------+ | ["marry", "Bob"] | +-----------------------------+- Return NULL value
{"age": 18, "name": "tom", "score": [100, 90, 87], "address" ": {"city": "Changsha", "province": "Hunan"}}The JSON path you are looking for does not exist
# age路径不存在,返回NULL # 若有多个路径,只要有一个路径存在则不会返回NULL select json_extract(content,'$.price') from test_json where id = 1; +---------------------------------+ | json_extract(content,'$.price') | +---------------------------------+ | NULL | +---------------------------------+
There are NULL
in the path# 存在任意路径为NULL则返回NULL select json_extract(content,'$.age',NULL) from test_json where id = 1; +------------------------------------+ | json_extract(content,'$.age',NULL) | +------------------------------------+ | NULL | +------------------------------------+
- Return error
If the first parameter is not JSON type data, return error
select json_extract('{1,2]',$[0])
If the path expression is not standardized, return error
select content->'$age' from test_json where id = 1; # 结果: ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 1.
5. Usage scenarios
The JSON_EXTRACT function is usually used when you want to obtain a specific data in JSON or use it as a judgment condition
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