mysql5.7版本開始支援JSON類型欄位
json_extract可以完全簡寫為->
json_unquote(json_extract())可以完全簡寫為->>
下面介紹大部分會利用簡寫
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"}]');
id | content |
---|---|
1 | # #{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “長沙”, “province”: “湖南”}}|
[1, “apple”, “red”, {“age”: 18, “name”: “tom”}] |
content:- 取得JSON數組中某個元素{“ age”: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “長沙”, “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 | +--------------------+
content:- 取得JSON中的巢狀資料結合前面介紹的兩種取得方式,可以取得json資料中的巢狀資料[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 | +------------------+
content: id=1四、漸入佳境#- 取得JSON多個路徑的資料將會將多個路徑的資料組合成陣列傳回{“age”: 18 , “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “長沙”, “province”: “湖南”}}
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 | +---------------------+
content: id=1- 路徑表達式*的使用將會將多個路徑的資料組合成陣列傳回{「age」: 18, “name”: “tom”, “score”: [100, 90, 87], “address”: {“city”: “長沙”, “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"] | +----------------------------------------------------------------------+
# 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- 傳回NULL值{「name ”: “tom”, “class”: {“id”: 3, “name”: “一年三班”}, “friend”: [{“age”: 20, “name”: “marry”}, {“age”: 21, “name”: “Bob”}], “address”: {“city”: “長沙”, “name”: “中央公園”}}
# 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"] | +-----------------------------+
content: id=1#尋找的JSON路徑都不存在{“age”: 18, “name”: “tom”, “score”: [100, 90, 87], "address ”: {“city”: “長沙”, “province”: “湖南”}}
# 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 | +---------------------------------+路徑中有NULL
#
# 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 | +------------------------------------+- 回傳錯誤若第一個參數不是JSON類型的數據,則回傳錯誤
select json_extract('{1,2]',$[0])若路徑表達式不規範,則傳回錯誤
select content->'$age' from test_json where id = 1; # 结果: ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 1.五、使用場景JSON_EXTRACT函數通常用於要取得JSON中某個特定的資料或要根據它作為判斷條件時使用
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