108 lines
2.7 KiB
Go
108 lines
2.7 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 plans
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import (
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"github.com/juju/errors"
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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/kv/memkv"
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"github.com/pingcap/tidb/plan"
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"github.com/pingcap/tidb/util/format"
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)
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var (
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_ plan.Plan = (*DistinctDefaultPlan)(nil)
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)
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// DistinctDefaultPlan e.g. SELECT distinct(id) FROM t;
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type DistinctDefaultPlan struct {
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*SelectList
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Src plan.Plan
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rows []*plan.Row
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cursor int
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}
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// Explain implements the plan.Plan Explain interface.
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func (r *DistinctDefaultPlan) Explain(w format.Formatter) {
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r.Src.Explain(w)
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w.Format("┌Compute distinct rows\n└Output field names %v\n", r.ResultFields)
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}
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// Filter implements the plan.Plan Filter interface.
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func (r *DistinctDefaultPlan) Filter(ctx context.Context, expr expression.Expression) (plan.Plan, bool, error) {
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return r, false, nil
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}
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// Next implements plan.Plan Next interface.
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func (r *DistinctDefaultPlan) Next(ctx context.Context) (row *plan.Row, err error) {
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if r.rows == nil {
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err = r.fetchAll(ctx)
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if err != nil {
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return nil, errors.Trace(err)
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}
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}
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if r.cursor == len(r.rows) {
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return
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}
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row = r.rows[r.cursor]
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updateRowStack(ctx, row.Data, row.FromData)
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r.cursor++
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return
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}
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func (r *DistinctDefaultPlan) fetchAll(ctx context.Context) error {
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t, err := memkv.CreateTemp(true)
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if err != nil {
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return errors.Trace(err)
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}
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defer func() {
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if derr := t.Drop(); derr != nil && err == nil {
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err = derr
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}
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}()
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for {
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row, err := r.Src.Next(ctx)
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if row == nil || err != nil {
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return errors.Trace(err)
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}
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var v []interface{}
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// get distinct key
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key := row.Data[0:r.HiddenFieldOffset]
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v, err = t.Get(key)
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if err != nil {
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return errors.Trace(err)
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}
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if len(v) == 0 {
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// no group for key, save data for this group
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r.rows = append(r.rows, row)
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if err := t.Set(key, []interface{}{true}); err != nil {
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return errors.Trace(err)
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}
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}
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}
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}
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// Close implements plan.Plan Close interface.
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func (r *DistinctDefaultPlan) Close() error {
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r.rows = nil
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r.cursor = 0
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return r.Src.Close()
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}
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