35 lines
1.2 KiB
Go
35 lines
1.2 KiB
Go
// Copyright 2015 PingCAP, Inc.
|
|
//
|
|
// 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,
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package optimizer
|
|
|
|
import "github.com/pingcap/tidb/ast"
|
|
|
|
// conditionNormalizer converts an condition expression into
|
|
// CNF(Conjunctive normal form).
|
|
// See https://en.wikipedia.org/wiki/Conjunctive_normal_form
|
|
// An boolean expression(usually a where condition) need to be converted
|
|
// to a series of AND conditions, so if a sub condition match an index,
|
|
// it can be pushed to that index to reduce cost.
|
|
// Ssub conditions that can not be pushed to index will be put into a Filter plan.
|
|
type conditionNormalizer struct {
|
|
}
|
|
|
|
func (b *conditionNormalizer) Enter(in ast.Node) (ast.Node, bool) {
|
|
return in, false
|
|
}
|
|
|
|
func (b *conditionNormalizer) Leave(in ast.Node) (ast.Node, bool) {
|
|
return in, true
|
|
}
|