MySQL操作之JSON数据类型操作详解

上一篇文章我们介绍了mysql数据存储过程参数实例详解，今天我们看看MySQL操作之JSON数据类型的相关内容。

概述

mysql自5.7.8版本开始，就支持了json结构的数据存储和查询，这表明了mysql也在不断的学习和增加nosql数据库的有点。但mysql毕竟是关系型数据库，在处理json这种非结构化的数据时，还是比较别扭的。

创建一个JSON字段的表

首先先创建一个表，这个表包含一个json格式的字段：

CREATE TABLE table_name (  id INT NOT NULL AUTO_INCREMENT,   json_col JSON,  PRIMARY KEY(id));

插入一条简单的JSON数据

INSERT INTO  table_name (json_col) VALUES  ('{"City": "Galle", "Description": "Best damn city in the world"}');

插入一条复杂的JSON数据

INSERT INTO table(col) VALUES('{"opening":"Sicilian","variations":["pelikan","dragon","najdorf"]}');

修改JSON数据

之前的例子中，我们插入了几条JSON数据，但是如果我们想修改JSON数据里的某个内容，怎么实现了？比如我们向 variations 数组里增加一个元素，可以这样：

UPDATE myjson SET dict=JSON_ARRAY_APPEND(dict,'$.variations','scheveningen') WHERE id = 2;

SELECT * FROM myjson

+----+-----------------------------------------------------------------------------------------+| id | dict                                          |+---+-----------------------------------------------------------------------------------------+| 2 | {"opening": "Sicilian", "variations": ["pelikan", "dragon", "najdorf", "scheveningen"]} |+----+-----------------------------------------------------------------------------------------+1 row in set (0.00 sec)

创建索引

MySQL的JSON格式数据不能直接创建索引，但是可以变通一下，把要搜索的数据单独拎出来，单独一个数据列，然后在这个字段上键一个索引。下面是官方的例子：

mysql> CREATE TABLE jemp (  ->   c JSON,  ->   g INT GENERATED ALWAYS AS (c->"$.id"),  ->   INDEX i (g)  -> );Query OK, 0 rows affected (0.28 sec)mysql> INSERT INTO jemp (c) VALUES   >  ('{"id": "1", "name": "Fred"}'), ('{"id": "2", "name": "Wilma"}'),   >  ('{"id": "3", "name": "Barney"}'), ('{"id": "4", "name": "Betty"}');Query OK, 4 rows affected (0.04 sec)Records: 4 Duplicates: 0 Warnings: 0mysql> SELECT c->>"$.name" AS name   >   FROM jemp WHERE g > 2;+--------+| name  |+--------+| Barney || Betty |+--------+2 rows in set (0.00 sec)mysql> EXPLAIN SELECT c->>"$.name" AS name   >  FROM jemp WHERE g > 2\G*************************** 1. row ***************************      id: 1 select_type: SIMPLE    table: jemp  partitions: NULL     type: rangepossible_keys: i     key: i   key_len: 5     ref: NULL     rows: 2   filtered: 100.00    Extra: Using where1 row in set, 1 warning (0.00 sec)mysql> SHOW WARNINGS\G*************************** 1. row *************************** Level: Note  Code: 1003Message: /* select#1 */ select json_unquote(json_extract(`test`.`jemp`.`c`,'$.name'))AS `name` from `test`.`jemp` where (`test`.`jemp`.`g` > 2)1 row in set (0.00 sec)

字符串转JSON格式

把json格式的字符串转换成MySQL的JSON类型:

SELECT CAST('[1,2,3]' as JSON) ;SELECT CAST('{"opening":"Sicilian","variations":["pelikan","dragon","najdorf"]}' as JSON);

Name	Description
JSON_APPEND()	Append data to JSON document
JSON_ARRAY()	Create JSON array
JSON_ARRAY_APPEND()	Append data to JSON document
JSON_ARRAY_INSERT()	Insert into JSON array-> Return value from JSON column after evaluating path; equivalent to JSON_EXTRACT().
JSON_CONTAINS()	Whether JSON document contains specific object at path
JSON_CONTAINS_PATH()	Whether JSON document contains any data at path
JSON_DEPTH()	Maximum depth of JSON document
JSON_EXTRACT()	Return data from JSON document->> Return value from JSON column after evaluating path and unquoting the result; equivalent to JSON_UNQUOTE(JSON_EXTRACT()).
JSON_INSERT()	Insert data into JSON document
JSON_KEYS()	Array of keys from JSON document
JSON_LENGTH()	Number of elements in JSON document
JSON_MERGE()	Merge JSON documents, preserving duplicate keys. Deprecated synonym for JSON_MERGE_PRESERVE()
JSON_MERGE_PRESERVE()	Merge JSON documents, preserving duplicate keys
JSON_OBJECT()	Create JSON object
JSON_QUOTE()	Quote JSON document
JSON_REMOVE()	Remove data from JSON document
JSON_REPLACE()	Replace values in JSON document
JSON_SEARCH()	Path to value within JSON document
JSON_SET()	Insert data into JSON document
JSON_TYPE()	Type of JSON value
JSON_UNQUOTE()	Unquote JSON value
JSON_VALID()	Whether JSON value is valid

总结

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