MariaDB: calculate the reads/writes ratio in percent
The Reads% and Writes% does not have the @totals until too late.  This should work better:

SELECT  Total,
       `Total reads`,
       `Total writes`,
       ROUND((@total_reads / @total_com * 100), 2) as `Reads %`,
       ROUND((@total_writes / @total_com * 100), 2) as `Writes %`
    FROM  
      ( SELECT  @total_com := SUM(IF(variable_name IN ('Com_select', 'Com_delete',
                             'Com_insert', 'Com_update', 'Com_replace'),
                             variable_value, 0)) AS `Total`,
                @total_reads := SUM(IF(variable_name = 'Com_select',
                                variable_value, 0)) AS `Total reads`,
                @total_writes := SUM(IF(variable_name IN ('Com_delete',
                                        'Com_insert', 'Com_update', 'Com_replace'
                          ), variable_value, 0)) as `Total writes`
            FROM  information_schema.GLOBAL_STATUS 
      ) x;