4b5f87c98a
Dual is a dummy table, `select 1, 2` is equivalent to `select 1, 2 from dual`, and dual is widely known.
92 lines
2.5 KiB
Go
92 lines
2.5 KiB
Go
// Copyright 2014 The ql Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSES/QL-LICENSE file.
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// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package rsets
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import (
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"strings"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/expression"
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"github.com/pingcap/tidb/field"
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"github.com/pingcap/tidb/plan"
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"github.com/pingcap/tidb/plan/plans"
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)
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var (
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_ plan.Planner = (*SelectFieldsRset)(nil)
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_ plan.Planner = (*SelectFromDualRset)(nil)
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)
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// SelectFieldsRset is record set to select fields.
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type SelectFieldsRset struct {
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Src plan.Plan
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SelectList *plans.SelectList
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}
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// Plan gets SrcPlan/SelectFieldsDefaultPlan.
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// If all fields are equal to src plan fields, then gets SrcPlan.
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// Default gets SelectFieldsDefaultPlan.
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func (r *SelectFieldsRset) Plan(ctx context.Context) (plan.Plan, error) {
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fields := r.SelectList.Fields
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srcFields := r.Src.GetFields()
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if len(fields) == len(srcFields) {
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match := true
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for i, v := range fields {
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// TODO: is it this check enough? e.g, the ident field is t.c.
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if x, ok := v.Expr.(*expression.Ident); ok && strings.EqualFold(x.L, srcFields[i].Name) && strings.EqualFold(v.Name, srcFields[i].Name) {
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continue
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}
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match = false
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break
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}
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if match {
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return r.Src, nil
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}
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}
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src := r.Src
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if x, ok := src.(*plans.TableDefaultPlan); ok {
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// check whether src plan will be set TableNilPlan, like `select 1, 2 from t`.
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isConst := true
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for _, v := range fields {
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if expression.FastEval(v.Expr) == nil {
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isConst = false
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break
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}
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}
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if isConst {
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src = &plans.TableNilPlan{T: x.T}
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}
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}
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p := &plans.SelectFieldsDefaultPlan{Src: src, SelectList: r.SelectList}
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return p, nil
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}
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// SelectFromDualRset is Recordset for select from dual, like `select 1, 1+1` or `select 1 from dual`.
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type SelectFromDualRset struct {
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Fields []*field.Field
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}
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// Plan gets SelectExprPlan.
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func (r *SelectFromDualRset) Plan(ctx context.Context) (plan.Plan, error) {
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return &plans.SelectFromDualPlan{Fields: r.Fields}, nil
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}
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