MySQL5.7新特性有哪些

小编给大家分享一下MySQL5.7新特性有哪些，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
 
 
6.1  优化(工具方面)增强
  5.7 版本中如果一个会话正在执行sql，且该sql 是支持explain的，那么我们可以通过指定会话id，查看该sql的执行计划。
 
EXPLAIN [options] FOR CONNECTION connection_id
该功能可以在一个会话里面查看另外一个会话中正在执行的长查询。
 
mysql> show processlist;
+----+-------------+-----------------+------+---------+------+--------------------------------------------------------+------------------+
| Id | User        | Host            | db   | Command | Time | State                                                  | Info             |
+----+-------------+-----------------+------+---------+------+--------------------------------------------------------+------------------+
| 1  | system user |                 | NULL | Connect | 78   | Connecting to master                                   | NULL             |
| 2  | system user |                 | NULL | Connect | 78   | Slave has read all relay log; waiting for more updates | NULL             |
| 3  | system user |                 | NULL | Connect | 78   | Waiting for an event from Coordinator                  | NULL             |
| 4  | system user |                 | NULL | Connect | 78   | Waiting for an event from Coordinator                  | NULL             |
| 5  | system user |                 | NULL | Connect | 78   | Waiting for an event from Coordinator                  | NULL             |
| 6  | system user |                 | NULL | Connect | 78   | Waiting for an event from Coordinator                  | NULL             |
| 8  | root        | localhost:47896 | NULL | Query   | 0    | starting                                               | show processlist |
| 9  | root        | localhost:47897 | NULL | Query   | 3    | User sleep                                             | select sleep(10) |
+----+-------------+-----------------+------+---------+------+--------------------------------------------------------+------------------+
8 rows in set (0.00 sec)
mysql> explain FOR CONNECTION  9;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
1 row in set (0.00 sec)
 
 
6.2 hint 功能增强
 相比于MySQL5.6版本的hint 主要是index 级别的hint和控制表join 顺序的hint,5.7.7之后，MySQL增加了优化器hint,来控制sql执行的方式，因为目前MySQL支持nest loop join，故暂时无hint来修改sql 的join方式。熟悉Oracle 的朋友是否会发现MySQL 和Oracle 在功能上越来越近了。话说回来5.7的hint (先别和 index hint 比较)的用法 ，和oracle 的类似:
 
SELECT /*+ NO_RANGE_OPTIMIZATION(t3 PRIMARY, f2_idx) */ f1 FROM t3 WHERE f1 > 30 AND f1 < 33;
SELECT /*+ BKA(t1) NO_BKA(t2) */ * FROM t1 INNER JOIN t2 WHERE ...;
SELECT /*+ NO_ICP(t1, t2) */ * FROM t1 INNER JOIN t2 WHERE ...;
SELECT /*+ SEMIJOIN(FIRSTMATCH, LOOSESCAN) */ * FROM t1 ...;
EXPLAIN SELECT /*+ NO_ICP(t1) */ * FROM t1 WHERE ...
优化器级别的hint分四种类型
 
Global: The hint affects the entire statement
Query block: The hint affects a particular query block within a statement ，什么是query block
(SELECT ... ) UNION (SELECT /*+ ... */ ... ) --后面的括号里面的称为 query block 。
Table-level: The hint affects a particular table within a query block
Index-level: The hint affects a particular index within a table
 
6.3 触发器功能增强
 5.7版本之前一个表 对于每种action(INSERT,UPDATE, DELETE)和时机(BEFORE or AFTER) 只能支持一种类型的触发器。新版本可以针对同一个action支持多个触发器。
 
6.4 syslog 功能
  之前的版本，*nix系统上的MySQL支持将错误日志发送到syslog是通过mysqld_safe捕获错误输出然后传递到syslog来实现的。新的版本原生支持将错误日志输出到syslog,且适用于windows系统，只需要通过简单的参数(log_syslog等)配置即可。参考 官方文档
  MySQL支持–syslog选项，可将在交互式模式下执行过的命令输出到syslog中（*nix系统下一般是.mysql_history）。对于匹配“ignore”过滤规则（可通过 –histignore选项或者 MYSQL_HISTIGNORE环境变量进行设置）的语句不会被记入。关于mysql客户端的日志使用参见：官方文档
6.5 虚拟列
在MySQL 5.7中，支持两种Generated Column，
1 Virtual Generated Column :只将Generated Column保存在数据字典中表的元数据，每次读取该列时进行计算，并不会将这一列数据持久化到磁盘上；
注意:MySQL 5.7.8 以前 虚拟列字段不支持创建索引。5.7.8之后Innodb支持在虚拟列创建辅助索引。
2 Stored Generated Column : 将Column持久化到存储，会占用一定的存储空间。与Virtual Column相比并没有明显的优势，因此，MySQL 5.7中，不指定Generated Column的类型，默认是Virtual Column。
创建虚拟列语法：
 
col_name data_type [GENERATED ALWAYS] AS (expression)
  [VIRTUAL | STORED] [UNIQUE [KEY]] [COMMENT comment]
  [[NOT] NULL] [[PRIMARY] KEY]
具体的例子
 
CREATE TABLE triangle (
  id int(10) not null primary key auto_increment,
  sidea DOUBLE,
  sideb DOUBLE,
  sidec DOUBLE AS (SQRT(sidea * sidea + sideb * sideb))
);
INSERT INTO triangle (sidea, sideb) VALUES(1,1),(3,4),(6,8),(12,16);
mysql> select * from  triangle;
+----+-------+-------+--------------------+
| id | sidea | sideb | sidec              |
+----+-------+-------+--------------------+
| 1  | 1     | 1     | 1.4142135623730951 |
| 2  | 3     | 4     | 5                  |
| 3  | 6     | 8     | 10                 |
| 4  | 12    | 16    | 20                 |
+----+-------+-------+--------------------+
4 rows in set (0.00 sec)
mysql> explain select * from  triangle where sidec > 10;
+----+-------------+----------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table    | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+----------+------------+------+---------------+------+---------+------+------+----------+-------------+
| 1  | SIMPLE      | triangle | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 4    | 33.33    | Using where |
+----+-------------+----------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
mysql> alter table triangle add key idx_sidec(sidec);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> explain select * from  triangle where sidec > 10;
+----+-------------+----------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
| id | select_type | table    | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra       |
+----+-------------+----------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
| 1  | SIMPLE      | triangle | NULL       | range | idx_sidec     | idx_sidec | 9       | NULL | 1    | 100.00   | Using where |
+----+-------------+----------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
看到这个例子,熟悉oracle的朋友可能会和函数索引作比较，两者比较类似.使用虚拟列达到函数索引或者解决业务上的设计缺陷，但是个人不建议使用类似的功能，因为虚拟列在一定程度上也会给后期运维带来潜在的风险和复杂度。网络上的例子基本都是使用虚拟列解决业务逻辑上的问题，违背了数据库只存储数据的初衷，思考一下MVC 框架的基本逻辑,业务逻辑要放到C 层或者V层，M层只存放数据即可。
 
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