SET @start_global_value = @@global.optimizer_switch;
SELECT @start_global_value;
@start_global_value
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
select @@global.optimizer_switch;
@@global.optimizer_switch
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
select @@session.optimizer_switch;
@@session.optimizer_switch
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
show global variables like 'optimizer_switch';
Variable_name	Value
optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
show session variables like 'optimizer_switch';
Variable_name	Value
optimizer_switch	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
select * from information_schema.global_variables where variable_name='optimizer_switch';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
select * from information_schema.session_variables where variable_name='optimizer_switch';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_SWITCH	index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
set global optimizer_switch=10;
set session optimizer_switch=5;
select @@global.optimizer_switch;
@@global.optimizer_switch
index_merge=off,index_merge_union=on,index_merge_sort_union=off,index_merge_intersection=on,engine_condition_pushdown=off
select @@session.optimizer_switch;
@@session.optimizer_switch
index_merge=on,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,engine_condition_pushdown=off
set global optimizer_switch="index_merge_sort_union=on";
set session optimizer_switch="index_merge=off";
select @@global.optimizer_switch;
@@global.optimizer_switch
index_merge=off,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=off
select @@session.optimizer_switch;
@@session.optimizer_switch
index_merge=off,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,engine_condition_pushdown=off
show global variables like 'optimizer_switch';
Variable_name	Value
optimizer_switch	index_merge=off,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=off
show session variables like 'optimizer_switch';
Variable_name	Value
optimizer_switch	index_merge=off,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,engine_condition_pushdown=off
select * from information_schema.global_variables where variable_name='optimizer_switch';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_SWITCH	index_merge=off,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=off
select * from information_schema.session_variables where variable_name='optimizer_switch';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_SWITCH	index_merge=off,index_merge_union=off,index_merge_sort_union=on,index_merge_intersection=off,engine_condition_pushdown=off
set session optimizer_switch="default";
select @@session.optimizer_switch;
@@session.optimizer_switch
index_merge=off,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=off
set global optimizer_switch=1.1;
ERROR 42000: Incorrect argument type to variable 'optimizer_switch'
set global optimizer_switch=1e1;
ERROR 42000: Incorrect argument type to variable 'optimizer_switch'
set session optimizer_switch="index_merge";
ERROR 42000: Variable 'optimizer_switch' can't be set to the value of 'index_merge'
set session optimizer_switch="foobar";
ERROR 42000: Variable 'optimizer_switch' can't be set to the value of 'foobar'
SET @@global.optimizer_switch = @start_global_value;
SELECT @@global.optimizer_switch;
@@global.optimizer_switch
index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on