How to get sum of the rows of 3 tables
http://searchoracle.techtarget.com/answer/Sum-of-two-table-row-counts-as-one-answer

 select ( select count(DISTINCT nom) from prodbiscuit WHERE status =2 )
 + ( select count(DISTINCT nom) from prodganache WHERE status =2 ) 
 + ( select count(DISTINCT nom) from prodmacaron) 
      as total_rows


Finally I've found it at given link