code: func (p *Limit) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan, error) {
  	// Limit forbids any condition to push down.
  	_, _, err := p.baseLogicalPlan.PredicatePushDown(nil)
  	return predicates, p, errors.Trace(err)
  }
docs: // PredicatePushDown implements LogicalPlan PredicatePushDown interface.