SET @start_global_value = @@global.sync_master_info; SELECT @start_global_value; # # exists as global only # select @@global.sync_master_info; --error ER_INCORRECT_GLOBAL_LOCAL_VAR select @@session.sync_master_info; show global variables like 'sync_master_info'; show session variables like 'sync_master_info'; select * from information_schema.global_variables where variable_name='sync_master_info'; select * from information_schema.session_variables where variable_name='sync_master_info'; # # show that it's writable # set global sync_master_info=1; select @@global.sync_master_info; --error ER_GLOBAL_VARIABLE set session sync_master_info=1; # # incorrect types # --error ER_WRONG_TYPE_FOR_VAR set global sync_master_info=1.1; --error ER_WRONG_TYPE_FOR_VAR set global sync_master_info=1e1; --error ER_WRONG_TYPE_FOR_VAR set global sync_master_info="foo"; # # min/max values # set global sync_master_info=0; select @@global.sync_master_info; set global sync_master_info=cast(-1 as unsigned int); select @@global.sync_master_info; SET @@global.sync_master_info = @start_global_value; SELECT @@global.sync_master_info;