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GRANT SESSION_VARIABLES_ADMIN ON *.* TO set_session_sysvars; REVOKE SYSTEM_VARIABLES_ADMIN ON *.* FROM set_session_sysvars; 

Modifying the role has an immediate effect: Any account granted the set_session_sysvars  role no longer has SYSTEM_VARIABLES_ADMIN  and is not able to set global system variables without being granted that ability explicitly. A similar GRANT / REVOKE  sequence can be applied to any account that was granted SYSTEM_VARIABLES_ADMIN  directly rather than by means of a role. 

## 5.1.9.2 Dynamic System Variables 

Many server system variables are dynamic and can be set at runtime. See Section 13.7.6.1, “SET Syntax for Variable Assignment” . For a description of the privilege requirements for setting system variables, see Section 5.1.9.1, “System Variable Privileges” 

The following table lists all dynamic system variables applicable within mysqld . 

The table lists each variable’s data type and scope. The last column indicates whether the scope for each variable is Global, Session, or both. Please see the corresponding item descriptions for details on setting and using the variables. Where appropriate, direct links to further information about the items are provided. 

Variables that have a type of “string”  take a string value. Variables that have a type of “numeric”  take a numeric value. Variables that have a type of “boolean”  can be set to 0, 1, ON  or OFF . Variables that are marked as “enumeration”  normally should be set to one of the available values for the variable, but can also be set to the number that corresponds to the desired enumeration value. For enumerated system variables, the first enumeration value corresponds to 0. This differs from the ENUM  data type used for table columns, for which the first enumeration value corresponds to 1. 

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