Mysql5.7的json存储以及sys schema是怎么样的
重点介绍新版本对JSON格式的支持。
1 支持JSON
从MySQL 5.7.8 开始，MySQL支持原生的JSON格式，即有独立的json类型，用于存放 json格式的数据。JSON 格式的数据并不是以string格式存储于数据库而是以内部的binary 格式，以便于快速的定位到json 格式中值。
在插入和更新操作时MySQL会对JSON 类型做校验，已检查数据是否符合json格式，如果不符合则报错。同时5.7.8 版本提供了四种JSON相关的函数，从而不用遍历全部数据。
a 创建: JSON_ARRAY(), JSON_MERGE(), JSON_OBJECT()
b 修改: JSON_APPEND(), JSON_ARRAY_APPEND(), JSON_ARRAY_INSERT(), JSON_INSERT(), JSON_QUOTE(), JSON_REMOVE(), JSON_REPLACE(), JSON_SET(), and JSON_UNQUOTE()
c 查询: JSON_CONTAINS(), JSON_CONTAINS_PATH(), JSON_EXTRACT(), JSON_KEYS(),JSON_SEARCH().
d 属性: JSON_DEPTH(), JSON_LENGTH(), JSON_TYPE() JSON_VALID().
我们通过简单的例子来对json有一定的认识。
创建
mysql>SELECT JSON_ARRAY('id',1,'name','dba@youzan');
+-------------------------------------------+
|JSON_ARRAY('id',1,'name','dba@youzan')|
+-------------------------------------------+
|["id",1,"name","dba@youzan"]|
+-------------------------------------------+
1 rowinset(0.00 sec)
mysql>SELECT JSON_OBJECT('id',1,'name','dba@youzan');
+--------------------------------------------+
|JSON_OBJECT('id',1,'name','dba@youzan')|
+--------------------------------------------+
|{"id":1,"name":"dba@youzan"}|
+--------------------------------------------+
1 rowinset(0.00 sec)
初始化
create table json_test(
idint(11)PRIMARY KEYNOTNULL auto_increment,
data json
)engine=innodb default charset=utf8;
insertintojson_test values(1,'{ "DBA": [ { "firstName": "yi", "lastName":"yang", "email": "dba@youzan.com" }],
"SA": [{ "firstName": "you", "lastName": "zan", "email": "sa@youzan.com" }],
"PE": [{ "firstName": "xiao", "lastName": "xiao", "email": "pe@youzan.com" }] }')
修改
mysql>select*from json_test \G
***************************1.row***************************
id:1
data:{"PE":[{"email":"pe@youzan.com","lastName":"xiao","firstName":"xiao"}],"SA":[{"email":"sa@youzan.com","lastName":"zan","firstName":"you"}],"DBA":[{"email":"dba@youzan.com","lastName":"yang","firstName":"yi"}]}
1 rowinset(0.00 sec)
mysql>update json_test set data=json_array_append(data,'$.DBA','{"email": "dba@youzan.com", "lastName": "yang", "firstName": "qilong"}')where id=1;
Query OK,1 row affected(0.01 sec)
Rows matched:1 Changed:1 Warnings:0
mysql>select*from json_test \G
***************************1.row***************************
id:1
data:{"PE":[{"email":"pe@youzan.com","lastName":"xiao","firstName":"xiao"}],"SA":[{"email":"sa@youzan.com","lastName":"zan","firstName":"you"}],"DBA":[{"email":"dba@youzan.com","lastName":"yang","firstName":"yi"},"{\"email\": \"dba@youzan.com\", \"lastName\": \"yang\", \"firstName\": \"qilong\"}"]}
1 rowinset(0.00 sec)
删除
mysql>update json_test set data=json_remove(data,'$.DBA[1]')where id=1;
Query OK,1 row affected(0.01 sec)
Rows matched:1 Changed:1 Warnings:0
mysql>select*from json_test \G
***************************1.row***************************
id:1
data:{"PE":[{"email":"pe@youzan.com","lastName":"xiao","firstName":"xiao"}],"SA":[{"email":"sa@youzan.com","lastName":"zan","firstName":"you"}],"DBA":[{"email":"dba@youzan.com","lastName":"yang","firstName":"yi"}]}
1 rowinset(0.00 sec)
-- 删除语句
update history_tab_sum set data=json_remove(data,'$."2017.11.28"') ;
-- 更新
-- update history_tab_sum set total=json_replace(total,'$."2017-11-28"',id);
-- 插入：
UPDATE history_tab_sum set data=JSON_MERGE(data,'{"2017-11-28":3344}') where id=10283;
-- append
update history_tab_sum set data=json_array_append(data,'$."2017-11-28"',id) where id=10283;
查看 json的key
mysql>SELECT id,json_keys(data)as"keys"FROM json_test;
+----+---------------------+
|id|keys|
+----+---------------------+
|1|["PE","SA","DBA"]|
+----+---------------------+
1 rowinset(0.00 sec)
查看DBA对应的值
mysql>SELECT id,json_extract(data,'$.DBA[0]')from json_test;
+----+--------------------------------------------------------------------+
|id|json_extract(data,'$.DBA[0]')|
+----+--------------------------------------------------------------------+
|1|{"email":"dba@youzan.com","lastName":"yang","firstName":"yi"}|
+----+--------------------------------------------------------------------+
1 rowinset(0.00 sec)
MySQL 5.7 版本提供的json格式以及对应的操作函数极丰富了MySQL的存储格式,可以在一定程度上和Mongodb和pg竞争，对于经常使用MySQL varchar 存储json的业务是一个福音。同时再强调一下对于OLTP业务的表结构设计 尽可能的避免大字段存储。一来是减少不必要的查询带来的IO，带宽，内存方面的影响 二来是 避免因为表大小太大导致的ddl 时间成本增加系统风险。
2 sys schema
MySQL 5.7 版本新增了sys 数据库,该库通过视图的形式把information_schema 和performance_schema结合起来，查询出更加令人容易理解的数据，帮助DBA快速获取数据库系统的各种纬度的元数据信息，帮助DBA和开发快速定位性能瓶颈。这里给两个例子能直观的了解sys 功能的强大。
mysql>select*from sys.schema_table_statistics limit 2\G
***************************1.row***************************
table_schema:yang
table_name:json_test
total_latency:1.81 ms
rows_fetched:21
fetch_latency:1.45 ms
rows_inserted:2
insert_latency:192.67 us
rows_updated:2
update_latency:166.94 us
rows_deleted:0
delete_latency:0 ps
io_read_requests:54
io_read:4.21 KiB
io_read_latency:289.37 us
io_write_requests:43
io_write:388.53 KiB
io_write_latency:703.51 us
io_misc_requests:75
io_misc_latency:40.02 ms
##直接查看未使用过的索引 ，方便吗？
mysql>SELECT*FROM schema_unused_indexes;
+---------------+-------------+------------+
|object_schema|object_name|index_name|
+---------------+-------------+------------+
|yang |t |idx_a|
|yang |yy |idx_nm|
+---------------+-------------+------------+
2 rowsinset(0.00 sec)