genmai.go
func (db *DB) Count(column ...interface{}) *Function {
	switch len(column) {
	case 0, 1:
		// do nothing.
	default:
		panic(fmt.Errorf("Count: a number of argument must be 0 or 1, got %v", len(column)))
	}
	return &Function{
		Name: "COUNT",
		Args: column,
	}
}
func (db *DB) Count(column ...interface{}) *Function {
	switch len(column) {
	case 0, 1:
		// do nothing.
	default:
		panic(fmt.Errorf("Count: a number of argument must be 0 or 1, got %v", len(column)))
	}
	return &Function{
		Name: "COUNT",
		Args: column,
	}
}
// Count returns "COUNT" function.