#
# show the global and session values;
#
select @@global.date_format;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
select @@session.date_format;
show global variables like 'date_format';
show session variables like 'date_format';
select * from information_schema.global_variables where variable_name='date_format';
select * from information_schema.session_variables where variable_name='date_format';

#
# show that it's read-only
#
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set global date_format="foo";
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set session date_format="foo";