// 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, // 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" ) type maxMinFunction struct { aggFunction isMax bool } // 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.CompareDatum(sc, &value) if err != nil { return err } if (mmf.isMax && c == -1) || (!mmf.isMax && c == 1) { value.Copy(&evalCtx.Value) } return nil }