To get all the server variables run this query either in the SQL window of your preferred interface (PHPMyAdmin or other) or in the MySQL CLI interface

SHOW VARIABLES;

You can specify if you want the session variables or the global variables as follows:

Session variables:

SHOW SESSION VARIABLES;

Global variables:

SHOW GLOBAL VARIABLES;

Like any other SQL command you can add parameters to your query such as the LIKE command:

SHOW [GLOBAL | SESSION] VARIABLES LIKE 'max_join_size';

Or, using wildcards:

SHOW [GLOBAL | SESSION] VARIABLES LIKE '%size%';

You can also filter the results of the SHOW query using a WHERE parameter as follows:

SHOW [GLOBAL | SESSION] VARIABLES WHERE VALUE > 0;