plan

type Plan interface {
	// Do iterates records and applies plan logic to the result set.
	// TODO: only get id or some fields.
	Do(ctx context.Context, f RowIterFunc) error
	// Explain the plan.
	Explain(w format.Formatter)
	// GetFields returns the result field list for a plan.
	GetFields() []*field.ResultField
	// Filter try to use index plan to reduce the result set.
	// If index can be used, a new index plan is returned, 'filtered' is true.
	// If no index can be used, the original plan is returned and 'filtered' return false.
	Filter(ctx context.Context, expr expression.Expression) (p Plan, filtered bool, err error)
}

type Planner interface {
	// Plan function returns Plan.
	Plan(ctx context.Context) (Plan, error)
}

type RowIterFunc func(id interface{}, data []interface{}) (more bool, err error)