config root man

#
# 2010-01-20 OBN Added check for I_S values after variable value changed
#

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

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

#
# show that it's writable
#
set global optimizer_switch=10;
set session optimizer_switch=5;
select @@global.optimizer_switch;
select @@session.optimizer_switch;
set global optimizer_switch="index_merge_sort_union=on";
set session optimizer_switch="index_merge=off";
select @@global.optimizer_switch;
select @@session.optimizer_switch;
show global variables like 'optimizer_switch';
show session variables like 'optimizer_switch';
--disable_warnings
select * from information_schema.global_variables where variable_name='optimizer_switch';
select * from information_schema.session_variables where variable_name='optimizer_switch';
--enable_warnings
set session optimizer_switch="default";
select @@session.optimizer_switch;

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

--echo #
--echo # Bug#59894 set optimizer_switch to e or d causes invalid
--echo # memory writes/valgrind warnings
--echo
set global optimizer_switch = 'def'; # means default
--error ER_WRONG_VALUE_FOR_VAR
set global optimizer_switch = 'e';

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