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56 lines
1.6 KiB
56 lines
1.6 KiB
// Copyright 2017 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package aggregation
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import (
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"github.com/pingcap/errors"
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"github.com/pingcap/tidb/sessionctx/stmtctx"
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"github.com/pingcap/tidb/types"
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"github.com/pingcap/tidb/util/chunk"
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)
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type firstRowFunction struct {
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aggFunction
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}
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// Update implements Aggregation interface.
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func (ff *firstRowFunction) Update(evalCtx *AggEvaluateContext, sc *stmtctx.StatementContext, row chunk.Row) error {
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if evalCtx.GotFirstRow {
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return nil
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}
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if len(ff.Args) != 1 {
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return errors.New("Wrong number of args for AggFuncFirstRow")
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}
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value, err := ff.Args[0].Eval(row)
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if err != nil {
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return err
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}
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value.Copy(&evalCtx.Value)
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evalCtx.GotFirstRow = true
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return nil
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}
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// GetResult implements Aggregation interface.
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func (ff *firstRowFunction) GetResult(evalCtx *AggEvaluateContext) types.Datum {
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return evalCtx.Value
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}
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func (ff *firstRowFunction) ResetContext(_ *stmtctx.StatementContext, evalCtx *AggEvaluateContext) {
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evalCtx.GotFirstRow = false
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}
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// GetPartialResult implements Aggregation interface.
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func (ff *firstRowFunction) GetPartialResult(evalCtx *AggEvaluateContext) []types.Datum {
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return []types.Datum{ff.GetResult(evalCtx)}
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}
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