【全局变量】mysql查看全局变量以及设置全局变量的值

1.查看mysql的所有全局变量的值

SHOW GLOBAL VARIABLES

或者

SHOW VARIABLES

mysql有很多全局变量，包括系统的一些基本信息，以及mysql的一些基本配置都可以在全局变量中查到。

2.查看mysql的单个全局变量的值

SHOW GLOBAL VARIABLES LIKE 'wait_timeout'

或者

SELECT @@wait_timeout

上面的查询也可以用模糊查询，与上面结果一样的模糊查询语句

SHOW GLOBAL VARIABLES LIKE 'wait_time%'
SHOW GLOBAL VARIABLES LIKE '%wait%'

注意:查看mysql的全局变量也可以不加global关键字，例如

SHOW VARIABLES
SHOW  VARIABLES LIKE '%wait%'
SHOW  VARIABLES LIKE 'wait_timeout'
SHOW  VARIABLES LIKE '%wait%'

3.设置全局变量的值

SET GLOBAL  wait_timeout = 604800;
SET @@GLOBAL.wait_timeout = 604800

SET GLOBAL event_scheduler = ON; 
SET @@global.event_scheduler = ON; 
SET GLOBAL event_scheduler = 1; 
SET @@global.event_scheduler = 1; 

注意:有的时候发现修改不生效，需要关闭会话重新启动，也就是退出一下重新登录。但是发现重新启动mysql服务器变量又不生效，最好的办法就是修改mysql启动的默认值。

(1)windows下C:ProgramDataMySQLMySQL Server 5.7my.ini，在[mysqld]栈下写下这个变量,例如修改mysql启动后默认开启任务调度(windows是修改my.ini文件)

　　修改:C:ProgramDataMySQLMySQL Server 5.7my.ini   (注意是ProgramData目录下的my.ini文件才能生效，如果修改C:Program FilesMySQLMySQL Server 5.7my-default.ini不会生效)

[mysqld]

# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin

# These are commonly set, remove the # and set as required.
# basedir = .....
# datadir = .....
# port = .....
# server_id = .....


# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M 

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES 
event_scheduler = 1

　　如果权限不够不能修改参考解决办法:http://www.cnblogs.com/qlqwjy/p/7989293.html

(2)linux下修改/etc/my.cnf,例如修改mysql默认任务调度开启和会话时长为7天

[root@iz2ze46xi6pjjj69ailg9lz ~]# vim /etc/my.cnf