tidb avg 源码
tidb avg 代码
文件路径：/expression/aggregation/avg.go
// Copyright 2017 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 aggregation
import (
"github.com/pingcap/tidb/parser/mysql"
"github.com/pingcap/tidb/parser/terror"
"github.com/pingcap/tidb/sessionctx/stmtctx"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/util/chunk"
"github.com/pingcap/tidb/util/mathutil"
)
type avgFunction struct {
aggFunction
}
func (af *avgFunction) updateAvg(sc *stmtctx.StatementContext, evalCtx *AggEvaluateContext, row chunk.Row) error {
a := af.Args[1]
value, err := a.Eval(row)
if err != nil {
return err
}
if value.IsNull() {
return nil
}
evalCtx.Value, err = calculateSum(sc, evalCtx.Value, value)
if err != nil {
return err
}
count, err := af.Args[0].Eval(row)
if err != nil {
return err
}
evalCtx.Count += count.GetInt64()
return nil
}
func (af *avgFunction) ResetContext(sc *stmtctx.StatementContext, evalCtx *AggEvaluateContext) {
if af.HasDistinct {
evalCtx.DistinctChecker = createDistinctChecker(sc)
}
evalCtx.Value.SetNull()
evalCtx.Count = 0
}
// Update implements Aggregation interface.
func (af *avgFunction) Update(evalCtx *AggEvaluateContext, sc *stmtctx.StatementContext, row chunk.Row) (err error) {
switch af.Mode {
case Partial1Mode, CompleteMode:
err = af.updateSum(sc, evalCtx, row)
case Partial2Mode, FinalMode:
err = af.updateAvg(sc, evalCtx, row)
case DedupMode:
panic("DedupMode is not supported now.")
}
return err
}
// GetResult implements Aggregation interface.
func (af *avgFunction) GetResult(evalCtx *AggEvaluateContext) (d types.Datum) {
switch evalCtx.Value.Kind() {
case types.KindFloat64:
sum := evalCtx.Value.GetFloat64()
d.SetFloat64(sum / float64(evalCtx.Count))
return
case types.KindMysqlDecimal:
x := evalCtx.Value.GetMysqlDecimal()
y := types.NewDecFromInt(evalCtx.Count)
to := new(types.MyDecimal)
err := types.DecimalDiv(x, y, to, types.DivFracIncr)
terror.Log(err)
frac := af.RetTp.GetDecimal()
if frac == -1 {
frac = mysql.MaxDecimalScale
}
err = to.Round(to, mathutil.Min(frac, mysql.MaxDecimalScale), types.ModeHalfUp)
terror.Log(err)
d.SetMysqlDecimal(to)
}
return
}
// GetPartialResult implements Aggregation interface.
func (af *avgFunction) GetPartialResult(evalCtx *AggEvaluateContext) []types.Datum {
return []types.Datum{types.NewIntDatum(evalCtx.Count), evalCtx.Value}
}
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