Write a short note on built in function in QBE?

Built in function in QBE: QBE involves various built in functions like AVG, MAX,MIN,SUM and CNT. We must prefix these operators along with ALL to create a multiset on that the aggregate operation is evaluated. The ALL operator ensures in which duplicates are not eliminated. We can use UNQ to specify which we want duplicates eliminated. QBE also offers the ability to calculate functions on groups of tuples by using the G operator, that is analogous to SQL's group by construct.