set session debug_dbug="L";
select @@global.debug_dbug="1";
@@global.debug_dbug="1"
0
select @@session.debug_dbug;
@@session.debug_dbug
L
show global variables like 'debug_dbug';
Variable_name	Value
debug_dbug	#
show session variables like 'debug_dbug';
Variable_name	Value
debug_dbug	L
select * from information_schema.global_variables where variable_name='debug_dbug';
VARIABLE_NAME	VARIABLE_VALUE
DEBUG_DBUG	#
select * from information_schema.session_variables where variable_name='debug_dbug';
VARIABLE_NAME	VARIABLE_VALUE
DEBUG_DBUG	L
set @@global.debug_dbug=1;
ERROR 42000: Incorrect argument type to variable 'debug_dbug'
set @@global.debug_dbug=1.1;
ERROR 42000: Incorrect argument type to variable 'debug_dbug'
set @@global.debug_dbug=1e1;
ERROR 42000: Incorrect argument type to variable 'debug_dbug'