A system variable can have a global value that affects server operation as a whole, a session value that affects only the current session, or both. To modify system variable runtime values, use the SET statement. See Section 13.7.4.1, “SET Syntax for Variable Assignment”. This section describes the privileges required to assign values to system variables at runtime.

Setting a global system variable runtime value requires the SUPER privilege.

To set a session system variable runtime value, use the SET SESSION statement. In contrast to setting global runtime values, setting session runtime values normally requires no special privileges and can be done by any user to affect the current session. For some system variables, setting the session value may have effects outside the current session and thus is a restricted operation that can be done only by users who have the SUPER privilege. If a session system variable is restricted in this way, the variable description indicates that restriction. Examples include binlog_format and sql_log_bin. Setting the session value of these variables affects binary logging for the current session, but may also have wider implications for the integrity of server replication and backups.