Well i have checked out the syntax for the databases for aggregate functions. I thought using the syntax similar to that of HSQL would be good. In it if we are having N tuples then we are computing the values for the N rows and then after that we make another call and return the value for the function. Well this seems very reasonable to do. Using PostgreSQL  we need to have two regular functions but if we have an aggregate function like Count(column_name) , then this would be done in just a single function , I guess we would not need two functions for it .