tidb func_lead_lag 源码
tidb func_lead_lag 代码
文件路径：/executor/aggfuncs/func_lead_lag.go
// Copyright 2019 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,
// 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 aggfuncs
import (
"unsafe"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/sessionctx"
"github.com/pingcap/tidb/util/chunk"
)
const (
// DefPartialResult4LeadLagSize is the size of partialResult4LeadLag
DefPartialResult4LeadLagSize = int64(unsafe.Sizeof(partialResult4LeadLag{}))
)
type baseLeadLag struct {
baseAggFunc
valueEvaluator // TODO: move it to partial result when parallel execution is supported.
defaultExpr expression.Expression
offset uint64
}
type partialResult4LeadLag struct {
rows []chunk.Row
curIdx uint64
}
func (v *baseLeadLag) AllocPartialResult() (pr PartialResult, memDelta int64) {
return PartialResult(&partialResult4LeadLag{}), DefPartialResult4LeadLagSize
}
func (v *baseLeadLag) ResetPartialResult(pr PartialResult) {
p := (*partialResult4LeadLag)(pr)
p.rows = p.rows[:0]
p.curIdx = 0
}
func (v *baseLeadLag) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) (memDelta int64, err error) {
p := (*partialResult4LeadLag)(pr)
p.rows = append(p.rows, rowsInGroup...)
memDelta += int64(len(rowsInGroup)) * DefRowSize
return memDelta, nil
}
type lead struct {
baseLeadLag
}
func (v *lead) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
p := (*partialResult4LeadLag)(pr)
var err error
if p.curIdx+v.offset < uint64(len(p.rows)) {
_, err = v.evaluateRow(sctx, v.args[0], p.rows[p.curIdx+v.offset])
} else {
_, err = v.evaluateRow(sctx, v.defaultExpr, p.rows[p.curIdx])
}
if err != nil {
return err
}
v.appendResult(chk, v.ordinal)
p.curIdx++
return nil
}
type lag struct {
baseLeadLag
}
func (v *lag) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
p := (*partialResult4LeadLag)(pr)
var err error
if p.curIdx >= v.offset {
_, err = v.evaluateRow(sctx, v.args[0], p.rows[p.curIdx-v.offset])
} else {
_, err = v.evaluateRow(sctx, v.defaultExpr, p.rows[p.curIdx])
}
if err != nil {
return err
}
v.appendResult(chk, v.ordinal)
p.curIdx++
return nil
}
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