set session debug_dbug="t";
show session variables like 'debug';
Variable_name	Value
debug	t
set session debug_dbug="t";
show session variables like 'debug';
Variable_name	Value
debug	t
set session debug_dbug="d:t";
show session variables like 'debug';
Variable_name	Value
debug	d:t
show session variables like 'debug';
Variable_name	Value
debug	t