--source include/have_optimizer_trace.inc

SET @start_global_value = @@global.optimizer_trace;
SELECT @start_global_value;

#
# exists as global and session
#
select @@global.optimizer_trace;
select @@session.optimizer_trace;
show global variables like 'optimizer_trace';
show session variables like 'optimizer_trace';
select * from information_schema.global_variables where variable_name='optimizer_trace';
select * from information_schema.session_variables where variable_name='optimizer_trace';

#
# show that it's writable
#
set global optimizer_trace=1;
select @@global.optimizer_trace;
set session optimizer_trace=1;
select @@session.optimizer_trace;
set global optimizer_trace=0;
select @@global.optimizer_trace;
set session optimizer_trace=0;
select @@session.optimizer_trace;
set session optimizer_trace=default;
select @@session.optimizer_trace;

#
# incorrect assignments
#
--error ER_WRONG_TYPE_FOR_VAR
set global optimizer_trace=1.1;
--error ER_WRONG_TYPE_FOR_VAR
set global optimizer_trace=1e1;
--error ER_WRONG_VALUE_FOR_VAR
set session optimizer_trace="foobar";

SET @@global.optimizer_trace = @start_global_value;
SELECT @@global.optimizer_trace;