github.com/whtcorpsinc/milevadb-prod@v0.0.0-20211104133533-f57f4be3b597/dbs/memristed/memex/aggregation/max_min.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 aggregation
    15  
    16  import (
    17  	"github.com/whtcorpsinc/milevadb/stochastikctx/stmtctx"
    18  	"github.com/whtcorpsinc/milevadb/types"
    19  	"github.com/whtcorpsinc/milevadb/soliton/chunk"
    20  )
    21  
    22  type maxMinFunction struct {
    23  	aggFunction
    24  	isMax bool
    25  }
    26  
    27  // GetResult implements Aggregation interface.
    28  func (mmf *maxMinFunction) GetResult(evalCtx *AggEvaluateContext) (d types.Causet) {
    29  	return evalCtx.Value
    30  }
    31  
    32  // GetPartialResult implements Aggregation interface.
    33  func (mmf *maxMinFunction) GetPartialResult(evalCtx *AggEvaluateContext) []types.Causet {
    34  	return []types.Causet{mmf.GetResult(evalCtx)}
    35  }
    36  
    37  // UFIDelate implements Aggregation interface.
    38  func (mmf *maxMinFunction) UFIDelate(evalCtx *AggEvaluateContext, sc *stmtctx.StatementContext, event chunk.Event) error {
    39  	a := mmf.Args[0]
    40  	value, err := a.Eval(event)
    41  	if err != nil {
    42  		return err
    43  	}
    44  	if evalCtx.Value.IsNull() {
    45  		value.Copy(&evalCtx.Value)
    46  	}
    47  	if value.IsNull() {
    48  		return nil
    49  	}
    50  	var c int
    51  	c, err = evalCtx.Value.CompareCauset(sc, &value)
    52  	if err != nil {
    53  		return err
    54  	}
    55  	if (mmf.isMax && c == -1) || (!mmf.isMax && c == 1) {
    56  		value.Copy(&evalCtx.Value)
    57  	}
    58  	return nil
    59  }