Try this instead:INSERT INTO query_builder (query_category , query_name , query_description , query_string ) VALUES ( 'email,newsletters', 'volunteers', 'Newsletter subscribers who are in the volunteer group', 'select c.customers_email_address, c.customers_lastname, c.customers_firstname, c.customers_group_pricing from TABLE_CUSTOMERS c where c.customers_newsletter = 1 AND c.customers_group_pricing = 4 GROUP BY c.customers_email_address order by c.customers_lastname, c.customers_firstname ASC');
And change the 4 to whatever number the "volunteers" group is. You can see that number in the URL in your admin area when you click on that group. (I think it shows as gID=XXXX in the URL.) (It also shows in the sidebar header when editing the group details.)
Also note that I took out the two \' marks around the \'1\' because they're not needed there.