#
# only global
#
select @@global.time_format;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
select @@session.time_format;
show global variables like 'time_format';
show session variables like 'time_format';
select * from information_schema.global_variables where variable_name='time_format';
select * from information_schema.session_variables where variable_name='time_format';

#
# show that it's read-only
#
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set global time_format=1;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set session time_format=1;