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

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