github.com/whtcorpsinc/milevadb-prod@v0.0.0-20211104133533-f57f4be3b597/interlock/aggfuncs/func_stddevsamp.go (about)

     1  // Copyright 2020 WHTCORPS INC, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package aggfuncs
    15  
    16  import (
    17  	"math"
    18  
    19  	"github.com/whtcorpsinc/milevadb/stochastikctx"
    20  	"github.com/whtcorpsinc/milevadb/soliton/chunk"
    21  )
    22  
    23  type stddevSamp4Float64 struct {
    24  	varPop4Float64
    25  }
    26  
    27  func (e *stddevSamp4Float64) AppendFinalResult2Chunk(sctx stochastikctx.Context, pr PartialResult, chk *chunk.Chunk) error {
    28  	p := (*partialResult4VarPopFloat64)(pr)
    29  	if p.count <= 1 {
    30  		chk.AppendNull(e.ordinal)
    31  		return nil
    32  	}
    33  	variance := p.variance / float64(p.count-1)
    34  	chk.AppendFloat64(e.ordinal, math.Sqrt(variance))
    35  	return nil
    36  }
    37  
    38  type stddevSamp4DistinctFloat64 struct {
    39  	varPop4DistinctFloat64
    40  }
    41  
    42  func (e *stddevSamp4DistinctFloat64) AppendFinalResult2Chunk(sctx stochastikctx.Context, pr PartialResult, chk *chunk.Chunk) error {
    43  	p := (*partialResult4VarPoFIDelistinctFloat64)(pr)
    44  	if p.count <= 1 {
    45  		chk.AppendNull(e.ordinal)
    46  		return nil
    47  	}
    48  	variance := p.variance / float64(p.count-1)
    49  	chk.AppendFloat64(e.ordinal, math.Sqrt(variance))
    50  	return nil
    51  }