aggfuncs: partially implement "AVG"

executor/aggfuncs/aggfuncs.go

@@ -23,9 +23,15 @@ import (
 
 // All the AggFunc implementations are listed here for navigation.
 var (
-// All the AggFunc implementations for "COUNT" are listed here.
-// All the AggFunc implementations for "SUM" are listed here.
-// All the AggFunc implementations for "AVG" are listed here.
+	// All the AggFunc implementations for "COUNT" are listed here.
+	// All the AggFunc implementations for "SUM" are listed here.
+	// All the AggFunc implementations for "AVG" are listed here.
+	_ AggFunc = (*avgOriginal4Decimal)(nil)
+	_ AggFunc = (*avgPartial4Decimal)(nil)
+
+	_ AggFunc = (*avgOriginal4Float64)(nil)
+	_ AggFunc = (*avgPartial4Float64)(nil)
+
 // All the AggFunc implementations for "FIRSTROW" are listed here.
 // All the AggFunc implementations for "MAX" are listed here.
 // All the AggFunc implementations for "MIN" are listed here.

executor/aggfuncs/builder.go

@@ -16,6 +16,7 @@ package aggfuncs
 import (
 	"github.com/pingcap/tidb/ast"
 	"github.com/pingcap/tidb/expression/aggregation"
+	"github.com/pingcap/tidb/mysql"
 )
 
 // Build is used to build a specific AggFunc implementation according to the
@@ -58,6 +59,42 @@ func buildSum(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
 
 // buildCount builds the AggFunc implementation for function "AVG".
 func buildAvg(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
+	base := baseAggFunc{
+		args:    aggFuncDesc.Args,
+		ordinal: ordinal,
+	}
+	switch aggFuncDesc.Mode {
+	// Build avg functions which consume the original data and remove the
+	// duplicated input of the same group.
+	case aggregation.DedupMode:
+		return nil // not implemented yet.
+
+	// Build avg functions which consume the original data and update their
+	// partial results.
+	case aggregation.CompleteMode, aggregation.Partial1Mode:
+		switch aggFuncDesc.Args[0].GetType().Tp {
+		case mysql.TypeNewDecimal:
+			if aggFuncDesc.HasDistinct {
+				return nil // not implemented yet.
+			}
+			return &avgOriginal4Decimal{baseAvgDecimal{base}}
+		case mysql.TypeFloat, mysql.TypeDouble:
+			if aggFuncDesc.HasDistinct {
+				return nil // not implemented yet.
+			}
+			return &avgOriginal4Float64{baseAvgFloat64{base}}
+		}
+
+	// Build avg functions which consume the partial result of other avg
+	// functions and update their partial results.
+	case aggregation.Partial2Mode, aggregation.FinalMode:
+		switch aggFuncDesc.Args[1].GetType().Tp {
+		case mysql.TypeNewDecimal:
+			return &avgPartial4Decimal{baseAvgDecimal{base}}
+		case mysql.TypeDouble:
+			return &avgPartial4Float64{baseAvgFloat64{base}}
+		}
+	}
 	return nil
 }
 

executor/aggfuncs/func_avg.go

@@ -0,0 +1,207 @@
+// Copyright 2018 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aggfuncs
+
+import (
+	"github.com/juju/errors"
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util/chunk"
+)
+
+// All the following avg function implementations return the decimal result,
+// which store the partial results in "partialResult4AvgDecimal".
+//
+// "baseAvgDecimal" is wrapped by:
+// - "avgOriginal4Decimal"
+// - "avgPartial4Decimal"
+type baseAvgDecimal struct {
+	baseAggFunc
+}
+
+type partialResult4AvgDecimal struct {
+	sum   types.MyDecimal
+	count int64
+}
+
+func (e *baseAvgDecimal) AllocPartialResult() PartialResult {
+	return PartialResult(&partialResult4AvgDecimal{})
+}
+
+func (e *baseAvgDecimal) ResetPartialResult(pr PartialResult) {
+	p := (*partialResult4AvgDecimal)(pr)
+	p.sum = *types.NewDecFromInt(0)
+	p.count = int64(0)
+}
+
+func (e *baseAvgDecimal) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
+	p := (*partialResult4AvgDecimal)(pr)
+	if p.count == 0 {
+		chk.AppendNull(e.ordinal)
+		return nil
+	}
+	decimalCount := types.NewDecFromInt(p.count)
+	finalResult := new(types.MyDecimal)
+	err := types.DecimalDiv(&p.sum, decimalCount, finalResult, types.DivFracIncr)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	chk.AppendMyDecimal(e.ordinal, finalResult)
+	return nil
+}
+
+type avgOriginal4Decimal struct {
+	baseAvgDecimal
+}
+
+func (e *avgOriginal4Decimal) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
+	p := (*partialResult4AvgDecimal)(pr)
+	newSum := new(types.MyDecimal)
+	for _, row := range rowsInGroup {
+		input, isNull, err := e.args[0].EvalDecimal(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		err = types.DecimalAdd(&p.sum, input, newSum)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		p.sum = *newSum
+		p.count++
+	}
+	return nil
+}
+
+type avgPartial4Decimal struct {
+	baseAvgDecimal
+}
+
+func (e *avgPartial4Decimal) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
+	p := (*partialResult4AvgDecimal)(pr)
+	newSum := new(types.MyDecimal)
+	for _, row := range rowsInGroup {
+		inputSum, isNull, err := e.args[1].EvalDecimal(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		inputCount, isNull, err := e.args[0].EvalInt(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		err = types.DecimalAdd(&p.sum, inputSum, newSum)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		p.sum = *newSum
+		p.count += inputCount
+	}
+	return nil
+}
+
+// All the following avg function implementations return the float64 result,
+// which store the partial results in "partialResult4AvgFloat64".
+//
+// "baseAvgFloat64" is wrapped by:
+// - "avgOriginal4Float64"
+// - "avgPartial4Float64"
+type baseAvgFloat64 struct {
+	baseAggFunc
+}
+
+type partialResult4AvgFloat64 struct {
+	sum   float64
+	count int64
+}
+
+func (e *baseAvgFloat64) AllocPartialResult() PartialResult {
+	return (PartialResult)(&partialResult4AvgFloat64{})
+}
+
+func (e *baseAvgFloat64) ResetPartialResult(pr PartialResult) {
+	p := (*partialResult4AvgFloat64)(pr)
+	p.sum = 0
+	p.count = 0
+}
+
+func (e *baseAvgFloat64) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
+	p := (*partialResult4AvgFloat64)(pr)
+	if p.count == 0 {
+		chk.AppendNull(e.ordinal)
+	} else {
+		chk.AppendFloat64(e.ordinal, p.sum/float64(p.count))
+	}
+	return nil
+}
+
+type avgOriginal4Float64 struct {
+	baseAvgFloat64
+}
+
+func (e *avgOriginal4Float64) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
+	p := (*partialResult4AvgFloat64)(pr)
+	for _, row := range rowsInGroup {
+		input, isNull, err := e.args[0].EvalReal(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		p.sum += input
+		p.count++
+	}
+	return nil
+}
+
+type avgPartial4Float64 struct {
+	baseAvgFloat64
+}
+
+func (e *avgPartial4Float64) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
+	p := (*partialResult4AvgFloat64)(pr)
+	for _, row := range rowsInGroup {
+		inputSum, isNull, err := e.args[1].EvalReal(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		inputCount, isNull, err := e.args[0].EvalInt(sctx, row)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		if isNull {
+			continue
+		}
+
+		p.sum += inputSum
+		p.count += inputCount
+	}
+	return nil
+}