func NewAvg(e sql.Expression) *Avg {
	return &Avg{expression.UnaryExpression{Child: e}}
}
NewAvg creates a new Avg node.
package aggregation
import (
	"fmt"
	"github.com/src-d/go-mysql-server/sql"
	"github.com/src-d/go-mysql-server/sql/expression"
)
type Avg struct {
	expression.UnaryExpression
}