一、前言mysql5.7版本开始支持json类型字段
json_extract可以完全简写为 ->
json_unquote(json_extract())可以完全简写为 ->>
下面介绍中大部分会利用简写
二、创建示例表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"}]');
idcontent
1 {“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “长沙”, “province”: “湖南”}}
2 [1, “apple”, “red”, {“age”: 18, “name”: “tom”}]
三、基本语法- 获取json对象中某个key对应的value值json_extract函数中，第一个参数content表示json数据，第二个参数为json路径，其中$表示该json数据本身，$.name就表示获取json中key为name的value值
可以利用 -> 表达式来代替json_extract
若获取的val本身为字符串，那么获取的val会被引号包起来，比如"tom"，这种数据被解析到程序对象中时，可能会被转义为\“tom\”。为了解决这个问题了，可以在外面再包上一层json_unquote函数，或者使用 ->> 代替->
content:
{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “长沙”, “province”: “湖南”}}
# 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tomselect 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 |+--------------------+
- 获取json数组中某个元素json_extract函数中，第一个参数content表示json数据，第二个参数为json路径，其中$表示该json数据本身，$[i]表示获取该json数组索引为i的元素（索引从0开始）
与获取key-val一样，若获取的元素为字符串，默认的方式也会得到双引号包起来的字符，导致程序转义，方法也是利用json_unquote函数，或者使用 ->> 代替->
content:
[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 |+------------------+
- 获取json中的嵌套数据结合前面介绍的两种获取方式，可以获取json数据中的嵌套数据
content: id=1
{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “长沙”, “province”: “湖南”}}
content: id=2
[1, “apple”, “red”, {“age”: 18, “name”: “tom”}]
# 得到:87select content->'$.score[2]' from test_json where id = 1;# 结果:+-----------------------+| content->'$.score[2]' |+-----------------------+| 87 |+-----------------------+# 得到:18select content->'$[3].age' from test_json where id = 2;# 结果:+---------------------+| content->'$[3].age' |+---------------------+| 18 |+---------------------+
四、渐入佳境- 获取json多个路径的数据将会把多个路径的数据组合成数组返回
content: id=1
{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “长沙”, “province”: “湖南”}}
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"] |+----------------------------------------------------------------------+
- 路径表达式*的使用将会把多个路径的数据组合成数组返回
# 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”: “一年三班”}, “friend”: [{“age”: 20, “name”: “marry”}, {“age”: 21, “name”: “bob”}], “address”: {“city”: “长沙”, “name”: “中央公园”}}
# 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nameselect 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"] |+-----------------------------+
- 返回null值content: id=1
{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “长沙”, “province”: “湖南”}}
寻找的json路径都不存在
# 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nullselect json_extract(content,'$.price') from test_json where id = 1;+---------------------------------+| json_extract(content,'$.price') |+---------------------------------+| null |+---------------------------------+
路径中有null
# 存在任意路径为null则返回nullselect json_extract(content,'$.age',null) from test_json where id = 1;+------------------------------------+| json_extract(content,'$.age',null) |+------------------------------------+| null |+------------------------------------+
- 返回错误若第一个参数不是json类型的数据，则返回错误
select json_extract('{1,2]',$[0])
若路径表达式不规范，则返回错误
select content->'$age' from test_json where id = 1;# 结果:error 3143 (42000): invalid json path expression. the error is around character position 1.
五、使用场景json_extract函数通常用于要获取json中某个特定的数据或者要根据它作为判断条件时使用
以上就是mysql中的json_extract怎么使用的详细内容。