SELECT @@GLOBAL.innodb_undo_directory; @@GLOBAL.innodb_undo_directory . . Expected SET @@GLOBAL.innodb_undo_directory="/tmp"; ERROR HY000: Variable 'innodb_undo_directory' is a read only variable Expected error 'Read only variable' SELECT COUNT(@@GLOBAL.innodb_undo_directory); COUNT(@@GLOBAL.innodb_undo_directory) 1 1 Expected SELECT VARIABLE_VALUE FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='innodb_undo_directory'; VARIABLE_VALUE . . Expected SELECT COUNT(@@GLOBAL.innodb_undo_directory); COUNT(@@GLOBAL.innodb_undo_directory) 1 1 Expected SELECT COUNT(VARIABLE_VALUE) FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='innodb_undo_directory'; COUNT(VARIABLE_VALUE) 1 1 Expected SELECT @@innodb_undo_directory = @@GLOBAL.innodb_undo_directory; @@innodb_undo_directory = @@GLOBAL.innodb_undo_directory 1 1 Expected SELECT COUNT(@@innodb_undo_directory); COUNT(@@innodb_undo_directory) 1 1 Expected SELECT COUNT(@@local.innodb_undo_directory); ERROR HY000: Variable 'innodb_undo_directory' is a GLOBAL variable Expected error 'Variable is a GLOBAL variable' SELECT COUNT(@@SESSION.innodb_undo_directory); ERROR HY000: Variable 'innodb_undo_directory' is a GLOBAL variable Expected error 'Variable is a GLOBAL variable' SELECT COUNT(@@GLOBAL.innodb_undo_directory); COUNT(@@GLOBAL.innodb_undo_directory) 1 1 Expected SELECT innodb_undo_directory = @@SESSION.innodb_undo_directory; ERROR 42S22: Unknown column 'innodb_undo_directory' in 'field list' Expected error 'Readonly variable'