The MySQL variable

MySQL variables:
Server variables:
Use parameters to change the MySQL run feature. The directive that is defined in the configuration file.

To view server variables:
mysql>show [GLOBAL] [SESSION] VARIABLES [like ' STRING '];
mysql> SELECT @@ global| [SESSION] STRING;

To modify a service variable:
Mysql>set global| SESSION string= ' VALUE ';

by Scope:
Global variables:
The variable has been in effect since the server started. No user settings are required.
Only users with full permissions can modify global variables.

Mysql>>show GLOBAL VARIABLES [like ' STRING '];


Session Variables:
Valid only for the current session and expire after the session is terminated.
Normal users can modify session variables.

Mysql>show [SESSION] VARIABLES [like ' STRING '];

According to the effective time division:
Dynamic adjustment:
It can be modified immediately and will take effect as soon as it is modified.

Global variables:
Invalid for the current session, only valid for newly established sessions.

Session Variables:
Takes effect immediately, but only valid for the current session.

Static adjustment:
The service needs to be restarted after the adjustment.
Can be written in a configuration file or passed to mysqld or mysqld-safe by parameters.

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The MySQL variable