select @@global.time_format;
@@global.time_format
%H:%i:%s
Warnings:
Warning	1287	'@@time_format' is deprecated and will be removed in a future release.
select @@session.time_format;
ERROR HY000: Variable 'time_format' is a GLOBAL variable
show global variables like 'time_format';
Variable_name	Value
time_format	%H:%i:%s
show session variables like 'time_format';
Variable_name	Value
time_format	%H:%i:%s
select * from information_schema.global_variables where variable_name='time_format';
VARIABLE_NAME	VARIABLE_VALUE
TIME_FORMAT	%H:%i:%s
select * from information_schema.session_variables where variable_name='time_format';
VARIABLE_NAME	VARIABLE_VALUE
TIME_FORMAT	%H:%i:%s
set global time_format=1;
ERROR HY000: Variable 'time_format' is a read only variable
set session time_format=1;
ERROR HY000: Variable 'time_format' is a read only variable
