Variance statistical function. 
 
Variance & operator=(const Variance &rhs)
 
TE_DEFINE_VISITABLE Variance(Expression *arg)
Constructor. 
 
A base class for unary functions. 
 
UnaryFunction & operator=(const UnaryFunction &rhs)
 
Expression * clone() const 
It creates a new copy of this expression. 
 
This is an abstract class that models a query expression. 
 
Variance statistical function.