tidb max_min 源码
tidb max_min 代码
文件路径：/expression/aggregation/max_min.go
// Copyright 2017 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 aggregation
import (
"github.com/pingcap/tidb/sessionctx/stmtctx"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/util/chunk"
"github.com/pingcap/tidb/util/collate"
)
type maxMinFunction struct {
aggFunction
isMax bool
ctor collate.Collator
}
// GetResult implements Aggregation interface.
func (mmf *maxMinFunction) GetResult(evalCtx *AggEvaluateContext) (d types.Datum) {
return evalCtx.Value
}
// GetPartialResult implements Aggregation interface.
func (mmf *maxMinFunction) GetPartialResult(evalCtx *AggEvaluateContext) []types.Datum {
return []types.Datum{mmf.GetResult(evalCtx)}
}
// Update implements Aggregation interface.
func (mmf *maxMinFunction) Update(evalCtx *AggEvaluateContext, sc *stmtctx.StatementContext, row chunk.Row) error {
a := mmf.Args[0]
value, err := a.Eval(row)
if err != nil {
return err
}
if evalCtx.Value.IsNull() {
value.Copy(&evalCtx.Value)
}
if value.IsNull() {
return nil
}
var c int
c, err = evalCtx.Value.Compare(sc, &value, mmf.ctor)
if err != nil {
return err
}
if (mmf.isMax && c == -1) || (!mmf.isMax && c == 1) {
value.Copy(&evalCtx.Value)
}
return nil
}
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