MySQL read/write ratio from information_schema.GLOBAL_STATUS
Use the typical trick of sum(IF the column is the right one, use it, if not read 0:

SELECT sum(IF(variable_name = 'Com_select', variable_value, 0)) as `Total reads`,
       sum(IF(variable_name IN ('Com_delete', 'Com_insert', 'Com_update', 'Com_replace'),
           variable_value, 0)) as `Total writes` 
FROM information_schema.GLOBAL_STATUS;