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reduce.go
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reduce.go
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 dataset
import (
"io"
)
import (
"github.com/pkg/errors"
)
import (
"github.com/arana-db/arana/pkg/mysql/rows"
"github.com/arana-db/arana/pkg/proto"
"github.com/arana-db/arana/pkg/reduce"
)
type ReduceDataset struct {
proto.Dataset
Reducers map[int]reduce.Reducer // field_index -> aggregator
prev []proto.Value
binary bool
eof bool
}
func (ad *ReduceDataset) Next() (proto.Row, error) {
if ad.eof {
return nil, io.EOF
}
nextRow, err := ad.Dataset.Next()
if errors.Is(err, io.EOF) {
if ad.prev == nil {
return nil, io.EOF
}
ad.eof = true
fields, _ := ad.Dataset.Fields()
if ad.binary {
return rows.NewBinaryVirtualRow(fields, ad.prev), nil
} else {
return rows.NewTextVirtualRow(fields, ad.prev), nil
}
}
if err != nil {
return nil, errors.WithStack(err)
}
fields, _ := ad.Fields()
values := make([]proto.Value, len(fields))
if err = nextRow.Scan(values); err != nil {
return nil, errors.WithStack(err)
}
if ad.prev == nil {
ad.prev = values
ad.binary = nextRow.IsBinary()
return ad.Next()
}
for i := range values {
red, ok := ad.Reducers[i]
if !ok {
continue
}
var (
prev = ad.prev[i]
next = values[i]
)
if next == nil {
continue
}
if prev == nil {
ad.prev[i] = next
continue
}
x, err := prev.Decimal()
if err != nil {
return nil, errors.WithStack(err)
}
y, err := next.Decimal()
if err != nil {
return nil, errors.WithStack(err)
}
z, err := red.Decimal(x, y)
if err != nil {
return nil, errors.WithStack(err)
}
ad.prev[i] = proto.NewValueDecimal(z)
}
return ad.Next()
}