SET @start_value = @@global.general_log_file;
SELECT @start_value;
@start_value
test.log
'#---------------------FN_DYNVARS_004_01-------------------------#'
SET @@global.general_log_file = DEFAULT;
SELECT RIGHT(@@global.general_log_file,10) AS log_file;
log_file
master.log
'#--------------------FN_DYNVARS_004_02------------------------#'
SET @@global.general_log_file = mytest.log;
ERROR 42000: Variable 'general_log_file' can't be set to the value of 'log'
'#----------------------FN_DYNVARS_004_03------------------------#'
SELECT @@global.general_log_file = VARIABLE_VALUE 
FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES 
WHERE VARIABLE_NAME='general_log_file';
@@global.general_log_file = VARIABLE_VALUE
1