tidb func_stddevsamp 源码
tidb func_stddevsamp 代码
文件路径：/executor/aggfuncs/func_stddevsamp.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 (
"math"
"github.com/pingcap/tidb/sessionctx"
"github.com/pingcap/tidb/util/chunk"
)
type stddevSamp4Float64 struct {
varPop4Float64
}
func (e *stddevSamp4Float64) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
p := (*partialResult4VarPopFloat64)(pr)
if p.count <= 1 {
chk.AppendNull(e.ordinal)
return nil
}
variance := p.variance / float64(p.count-1)
chk.AppendFloat64(e.ordinal, math.Sqrt(variance))
return nil
}
type stddevSamp4DistinctFloat64 struct {
varPop4DistinctFloat64
}
func (e *stddevSamp4DistinctFloat64) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
p := (*partialResult4VarPopDistinctFloat64)(pr)
if p.count <= 1 {
chk.AppendNull(e.ordinal)
return nil
}
variance := p.variance / float64(p.count-1)
chk.AppendFloat64(e.ordinal, math.Sqrt(variance))
return nil
}
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