89 lines
2.4 KiB
Go
89 lines
2.4 KiB
Go
// 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/juju/errors"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/expression"
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"github.com/pingcap/tidb/sessionctx/stmtctx"
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"github.com/pingcap/tidb/types"
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)
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type maxMinFunction struct {
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aggFunction
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isMax bool
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}
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// Clone implements Aggregation interface.
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func (mmf *maxMinFunction) Clone() Aggregation {
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nf := *mmf
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for i, arg := range mmf.Args {
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nf.Args[i] = arg.Clone()
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}
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return &nf
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}
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// CalculateDefaultValue implements Aggregation interface.
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func (mmf *maxMinFunction) CalculateDefaultValue(schema *expression.Schema, ctx context.Context) (d types.Datum, valid bool) {
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arg := mmf.Args[0]
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result := expression.EvaluateExprWithNull(ctx, schema, arg)
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if con, ok := result.(*expression.Constant); ok {
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return con.Value, true
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}
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return d, false
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}
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// GetType implements Aggregation interface.
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func (mmf *maxMinFunction) GetType() *types.FieldType {
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return mmf.Args[0].GetType()
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}
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// GetResult implements Aggregation interface.
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func (mmf *maxMinFunction) GetResult(ctx *AggEvaluateContext) (d types.Datum) {
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return ctx.Value
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}
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// GetPartialResult implements Aggregation interface.
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func (mmf *maxMinFunction) GetPartialResult(ctx *AggEvaluateContext) []types.Datum {
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return []types.Datum{mmf.GetResult(ctx)}
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}
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// Update implements Aggregation interface.
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func (mmf *maxMinFunction) Update(ctx *AggEvaluateContext, sc *stmtctx.StatementContext, row types.Row) error {
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if len(mmf.Args) != 1 {
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return errors.New("Wrong number of args for AggFuncMaxMin")
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}
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a := mmf.Args[0]
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value, err := a.Eval(row)
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if err != nil {
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return errors.Trace(err)
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}
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if ctx.Value.IsNull() {
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ctx.Value = value
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}
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if value.IsNull() {
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return nil
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}
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var c int
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c, err = ctx.Value.CompareDatum(sc, &value)
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if err != nil {
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return errors.Trace(err)
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}
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if (mmf.isMax && c == -1) || (!mmf.isMax && c == 1) {
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ctx.Value = value
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}
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return nil
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}
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