func MAX(expr interface{}) Expr {
	return aggregateFor("MAX", expr)
}
MAX creates an Expr that keeps track of the maximum value of the wrapped
expression or field.
package expr
func init() {
	registerAggregate("SUM", func(wasSet bool, current float64, next float64) float64 {
		return current + next
	}, func(wasSet bool, current float64, next float64) float64 {
		return current + next
	})
	registerAggregate("MIN", func(wasSet bool, current float64, next float64) float64 {
		if !wasSet {
			return next
		}
		if next < current {
			return next
		}
		return current
	}, func(wasSet bool, current float64, next float64) float64 {
		if !wasSet {
			return next
		}
		if next < current {
			return next
		}
		return current
	})
	registerAggregate("MAX", func(wasSet bool, current float64, next float64) float64 {
		if !wasSet {
			return next
		}
		if next > current {
			return next
		}
		return current
	}, func(wasSet bool, current float64, next float64) float64 {
		if !wasSet {
			return next
		}
		if next > current {
			return next
		}
		return current
	})
	registerAggregate("COUNT", func(wasSet bool, current float64, next float64) float64 {
		return current + 1
	}, func(wasSet bool, current float64, next float64) float64 {
		return current + next
	})
}
func SUM(expr interface{}) Expr {
	return aggregateFor("SUM", expr)
}
func MIN(expr interface{}) Expr {
	return aggregateFor("MIN", expr)
}