mysql中json_extract函数的使用?作用是什么?

需求描述:

　　今天看mysql中的json数据类型,涉及到一些使用,使用到了函数json_extract来

　　获取json字段中某个key的值,在此记录下.

操作过程:

1.查看包含json字段的表信息

mysql> desc tab_json;
+-------+------------+------+-----+---------+----------------+
| Field | Type       | Null | Key | Default | Extra          |
+-------+------------+------+-----+---------+----------------+
| id    | bigint(20) | NO   | PRI | NULL    | auto_increment |
| data  | json       | YES  |     | NULL    |                |
+-------+------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> show create table tab_json;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tab_json | CREATE TABLE `tab_json` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `data` json DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select * from tab_json;
+----+----------------------------------------------------------------+
| id | data                                                           |
+----+----------------------------------------------------------------+
|  1 | {"Tel": "132223232444", "name": "david", "address": "Beijing"} |
|  2 | {"Tel": "13390989765", "name": "Mike", "address": "Guangzhou"} |
+----+----------------------------------------------------------------+
2 rows in set (0.00 sec)

备注:data字段就是json的数据类型,由键值对组成.

2.json_extract函数的使用

mysql> select json_extract('{"name":"Zhaim","tel":"13240133388"}',"$.tel");
+--------------------------------------------------------------+
| json_extract('{"name":"Zhaim","tel":"13240133388"}',"$.tel") |
+--------------------------------------------------------------+
| "13240133388"                                                |
+--------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select json_extract('{"name":"Zhaim","tel":"13240133388"}',"$.name");
+---------------------------------------------------------------+
| json_extract('{"name":"Zhaim","tel":"13240133388"}',"$.name") |
+---------------------------------------------------------------+
| "Zhaim"                                                       |
+---------------------------------------------------------------+
1 row in set (0.00 sec)

备注:这个查询时直接对json对象进行操作.

3.对tab_json表使用json_extract函数

mysql> select json_extract(data,'$.name') from tab_json;
+-----------------------------+
| json_extract(data,'$.name') |
+-----------------------------+
| "david"                     |
| "Mike"                      |
+-----------------------------+
2 rows in set (0.00 sec)

mysql> select json_extract(data,'$.name'),json_extract(data,'$.tel') from tab_json;  #如果查询没有的key,那么是可以查询,不过返回的是NULL.
+-----------------------------+----------------------------+
| json_extract(data,'$.name') | json_extract(data,'$.tel') |
+-----------------------------+----------------------------+
| "david"                     | NULL                       |
| "Mike"                      | NULL                       |
+-----------------------------+----------------------------+
2 rows in set (0.00 sec)

mysql> select json_extract(data,'$.name'),json_extract(data,'$.address') from tab_json;
+-----------------------------+--------------------------------+
| json_extract(data,'$.name') | json_extract(data,'$.address') |
+-----------------------------+--------------------------------+
| "david"                     | "Beijing"                      |
| "Mike"                      | "Guangzhou"                    |
+-----------------------------+--------------------------------+
2 rows in set (0.00 sec)

备注:通过json_extract函数,获取到了json对象的特定key的值.