1select @@global.extra_port; 2@@global.extra_port 30 4select @@session.extra_port; 5ERROR HY000: Variable 'extra_port' is a GLOBAL variable 6show global variables like 'extra_port'; 7Variable_name Value 8extra_port 0 9show session variables like 'extra_port'; 10Variable_name Value 11extra_port 0 12select * from information_schema.global_variables where variable_name='extra_port'; 13VARIABLE_NAME VARIABLE_VALUE 14EXTRA_PORT 0 15Warnings: 16Warning 1287 'INFORMATION_SCHEMA.GLOBAL_VARIABLES' is deprecated and will be removed in a future release. Please use performance_schema.global_variables instead 17select * from information_schema.session_variables where variable_name='extra_port'; 18VARIABLE_NAME VARIABLE_VALUE 19EXTRA_PORT 0 20Warnings: 21Warning 1287 'INFORMATION_SCHEMA.SESSION_VARIABLES' is deprecated and will be removed in a future release. Please use performance_schema.session_variables instead 22set global extra_port=1; 23ERROR HY000: Variable 'extra_port' is a read only variable 24set session extra_port=1; 25ERROR HY000: Variable 'extra_port' is a read only variable 26