System variables start with two

at signs

-

@

. Shows base directory of MySQL

SELECT @@basedir

Shows whether query uses cache or not

SELECT @@have_query_cache

Shows what size does query cache have

SELECT @@query_cache_size

... Shows complete list of system variables with their values

SHOW VARIABLES

Complete list of system variables using

phpmyadmin

: phpmyadmin/server_variables.php