zero.go

// Copyright 2016 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.

package sql

import (
	"golang.org/x/net/context"

	"github.com/cockroachdb/cockroach/pkg/sql/parser"
)

// zeroNode is a planNode with no columns and no rows and is used for nodes that
// have no results. (e.g. a table for which the filtering condition has a
// contradiction)
type zeroNode struct {
	// We use planNodes as map keys, and zero-size structs are optimized to all
	// point to the same location in memory. As a result, unless we include some
	// field in this struct every zeroNode will have the same identity.
	// In particular, the parallelization detector maps planNodes to go channels
	// which this causes problems for (see TestParallelizeQueueNoDependencies).
	_ interface{}
}

func (*zeroNode) Values() parser.Datums { return nil }
func (*zeroNode) Start(runParams) error { return nil }
func (*zeroNode) Close(context.Context) {}

func (z *zeroNode) Next(runParams) (bool, error) {
	return false, nil
}