sample

type Sample struct {

	// it determines which sample action (random sample by rows / percents, sample by order and so on) to take.
	Type int
	// UsingBlock is used to speed up the sample process but will cause centroids skewed.
	// If true, the sample action will randomly stop the sample process after it has sampled enough rows.
	UsingBlock bool
	// NeedOutputRowSeen indicates whether the sample operator needs to output the count of row seen as the last column.
	NeedOutputRowSeen bool

	Rows     int
	Percents float64

	// sample(expression1, expression2, ..., number)'s expression.
	SampleExprs []*plan.Expr

	// group by expr1, expr2 ...
	GroupExprs []*plan.Expr

	vm.OperatorBase
	// contains filtered or unexported fields
}