github.com/whtcorpsinc/milevadb-prod@v0.0.0-20211104133533-f57f4be3b597/dbs/memristed/memex/aggregation/first_row.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/errors"
    18  	"github.com/whtcorpsinc/milevadb/stochastikctx/stmtctx"
    19  	"github.com/whtcorpsinc/milevadb/types"
    20  	"github.com/whtcorpsinc/milevadb/soliton/chunk"
    21  )
    22  
    23  type firstEventFunction struct {
    24  	aggFunction
    25  }
    26  
    27  // UFIDelate implements Aggregation interface.
    28  func (ff *firstEventFunction) UFIDelate(evalCtx *AggEvaluateContext, sc *stmtctx.StatementContext, event chunk.Event) error {
    29  	if evalCtx.GotFirstEvent {
    30  		return nil
    31  	}
    32  	if len(ff.Args) != 1 {
    33  		return errors.New("Wrong number of args for AggFuncFirstEvent")
    34  	}
    35  	value, err := ff.Args[0].Eval(event)
    36  	if err != nil {
    37  		return err
    38  	}
    39  	value.Copy(&evalCtx.Value)
    40  	evalCtx.GotFirstEvent = true
    41  	return nil
    42  }
    43  
    44  // GetResult implements Aggregation interface.
    45  func (ff *firstEventFunction) GetResult(evalCtx *AggEvaluateContext) types.Causet {
    46  	return evalCtx.Value
    47  }
    48  
    49  func (ff *firstEventFunction) ResetContext(_ *stmtctx.StatementContext, evalCtx *AggEvaluateContext) {
    50  	evalCtx.GotFirstEvent = false
    51  }
    52  
    53  // GetPartialResult implements Aggregation interface.
    54  func (ff *firstEventFunction) GetPartialResult(evalCtx *AggEvaluateContext) []types.Causet {
    55  	return []types.Causet{ff.GetResult(evalCtx)}
    56  }