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MySQL 5.6 Reference Manual
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MySQL 5.6 Reference Manual  /  ...  /  System Variable Privileges System Variable Privileges

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

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

To set a session system variable at runtime, use the SET SESSION statement. In contrast to global system variable values, setting session system variable values at runtime normally requires no special privileges and can be done by any user to affect the current session. However, for some system variables, setting the session value can 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, sql_log_bin, and sql_log_off.

The reason for restricting certain session system variables is that changing them can have an effect beyond the current session. For example, setting the session binlog_format or sql_log_bin value affects binary logging for the current session, but that may have implications for the integrity of server replication and backups.