SET @start_global_value = @@global.optimizer_trace;
SELECT @start_global_value;
@start_global_value
enabled=off,one_line=off
select @@global.optimizer_trace;
@@global.optimizer_trace
enabled=off,one_line=off
select @@session.optimizer_trace;
@@session.optimizer_trace
enabled=off,one_line=off
show global variables like 'optimizer_trace';
Variable_name	Value
optimizer_trace	enabled=off,one_line=off
show session variables like 'optimizer_trace';
Variable_name	Value
optimizer_trace	enabled=off,one_line=off
select * from information_schema.global_variables where variable_name='optimizer_trace';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_TRACE	enabled=off,one_line=off
select * from information_schema.session_variables where variable_name='optimizer_trace';
VARIABLE_NAME	VARIABLE_VALUE
OPTIMIZER_TRACE	enabled=off,one_line=off
set global optimizer_trace=1;
select @@global.optimizer_trace;
@@global.optimizer_trace
enabled=on,one_line=off
set session optimizer_trace=1;
select @@session.optimizer_trace;
@@session.optimizer_trace
enabled=on,one_line=off
set global optimizer_trace=0;
select @@global.optimizer_trace;
@@global.optimizer_trace
enabled=off,one_line=off
set session optimizer_trace=0;
select @@session.optimizer_trace;
@@session.optimizer_trace
enabled=off,one_line=off
set session optimizer_trace=default;
select @@session.optimizer_trace;
@@session.optimizer_trace
enabled=off,one_line=off
set global optimizer_trace=1.1;
ERROR 42000: Incorrect argument type to variable 'optimizer_trace'
set global optimizer_trace=1e1;
ERROR 42000: Incorrect argument type to variable 'optimizer_trace'
set session optimizer_trace="foobar";
ERROR 42000: Variable 'optimizer_trace' can't be set to the value of 'foobar'
SET @@global.optimizer_trace = @start_global_value;
SELECT @@global.optimizer_trace;
@@global.optimizer_trace
enabled=off,one_line=off