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