forked from dolthub/go-mysql-server
/
avg.go
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/
avg.go
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// Copyright 2020-2021 Dolthub, 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 (
"fmt"
"github.com/Sndav/go-mysql-server/sql"
"github.com/Sndav/go-mysql-server/sql/expression"
)
// Avg node to calculate the average from numeric column
type Avg struct {
expression.UnaryExpression
}
var _ sql.FunctionExpression = (*Avg)(nil)
// NewAvg creates a new Avg node.
func NewAvg(ctx *sql.Context, e sql.Expression) *Avg {
return &Avg{expression.UnaryExpression{Child: e}}
}
// FunctionName implements sql.FunctionExpression
func (a *Avg) FunctionName() string {
return "avg"
}
func (a *Avg) String() string {
return fmt.Sprintf("AVG(%s)", a.Child)
}
// Type implements AggregationExpression interface. (AggregationExpression[Expression]])
func (a *Avg) Type() sql.Type {
return sql.Float64
}
// IsNullable implements AggregationExpression interface. (AggregationExpression[Expression]])
func (a *Avg) IsNullable() bool {
return true
}
// Eval implements AggregationExpression interface. (AggregationExpression[Expression]])
func (a *Avg) Eval(ctx *sql.Context, buffer sql.Row) (interface{}, error) {
// This case is triggered when no rows exist.
if buffer[0] == float64(0) && buffer[1] == int64(0) {
return nil, nil
}
sum := buffer[0].(float64)
rows := buffer[1].(int64)
if rows == 0 {
return float64(0), nil
}
return sum / float64(rows), nil
}
// WithChildren implements the Expression interface.
func (a *Avg) WithChildren(ctx *sql.Context, children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(a, len(children), 1)
}
return NewAvg(ctx, children[0]), nil
}
// NewBuffer implements AggregationExpression interface. (AggregationExpression)
func (a *Avg) NewBuffer() sql.Row {
const (
sum = float64(0)
rows = int64(0)
)
return sql.NewRow(sum, rows)
}
// Update implements AggregationExpression interface. (AggregationExpression)
func (a *Avg) Update(ctx *sql.Context, buffer, row sql.Row) error {
v, err := a.Child.Eval(ctx, row)
if err != nil {
return err
}
if v == nil {
return nil
}
v, err = sql.Float64.Convert(v)
if err != nil {
v = float64(0)
}
buffer[0] = buffer[0].(float64) + v.(float64)
buffer[1] = buffer[1].(int64) + 1
return nil
}
// Merge implements AggregationExpression interface. (AggregationExpression)
func (a *Avg) Merge(ctx *sql.Context, buffer, partial sql.Row) error {
bsum := buffer[0].(float64)
brows := buffer[1].(int64)
psum := partial[0].(float64)
prows := partial[1].(int64)
buffer[0] = bsum + psum
buffer[1] = brows + prows
return nil
}