protected virtual Expression VisitConstraint(SqlConstraintExpression expression)
        {
            var referencesExpression = (SqlReferencesExpression)Visit(expression.ReferencesExpression);

            if (referencesExpression != expression.ReferencesExpression)
            {
                return(expression.ChangeReferences(referencesExpression));
            }
            else
            {
                return(expression);
            }
        }