[MySQL] AVG

[optime]

SELECT 
   tb1.campo1, 
   tb1.campo2, 
   tb1.campo3, 
   COUNT( * ) AS TOTALE1, 
   COUNT( tb2.campo1 ) AS TOTALE2, 
   COUNT( * ) / COUNT( tb2.campo1 ) * 100 AS PERC 
FROM 
   ...