module Arel::Expressions

def average
  Nodes::Avg.new [self]
end

def count(distinct = false)
  Nodes::Count.new [self], distinct
end

def extract(field)
  Nodes::Extract.new [self], field
end

def maximum
  Nodes::Max.new [self]
end

def minimum
  Nodes::Min.new [self]
end

def sum
  Nodes::Sum.new [self]
end