What is aggregate function? Briefly describe it?

Aggregate functions are functions that take a collection of values as input and return a one value. SQL offers 5 built-in aggregate functions:

a)      Average: avg

b)      Minimum:min

c)       Maximum: max

d)      Total:sum

e)      Count:count

Average: avg

Select avg (balance)

From account

Where branch-name='perryridge'

Count :count

Select branch-name,count(distinct customer-name)

From depositior,account

Where depositor.account-number=account.account-number

groupby branch-name