/
first_row.go
82 lines (73 loc) · 2.33 KB
/
first_row.go
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// 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 (
log "github.com/Sirupsen/logrus"
"github.com/juju/errors"
"github.com/pingcap/tidb/context"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/sessionctx/variable"
"github.com/pingcap/tidb/util/types"
)
type firstRowFunction struct {
aggFunction
}
// Clone implements Aggregation interface.
func (ff *firstRowFunction) Clone() Aggregation {
nf := *ff
for i, arg := range ff.Args {
nf.Args[i] = arg.Clone()
}
return &nf
}
// GetType implements Aggregation interface.
func (ff *firstRowFunction) GetType() *types.FieldType {
return ff.Args[0].GetType()
}
// Update implements Aggregation interface.
func (ff *firstRowFunction) Update(ctx *AggEvaluateContext, sc *variable.StatementContext, row []types.Datum) error {
if ctx.GotFirstRow {
return nil
}
if len(ff.Args) != 1 {
return errors.New("Wrong number of args for AggFuncFirstRow")
}
value, err := ff.Args[0].Eval(row)
if err != nil {
return errors.Trace(err)
}
ctx.Value = value
ctx.GotFirstRow = true
return nil
}
// GetResult implements Aggregation interface.
func (ff *firstRowFunction) GetResult(ctx *AggEvaluateContext) types.Datum {
return ctx.Value
}
// GetPartialResult implements Aggregation interface.
func (ff *firstRowFunction) GetPartialResult(ctx *AggEvaluateContext) []types.Datum {
return []types.Datum{ff.GetResult(ctx)}
}
// CalculateDefaultValue implements Aggregation interface.
func (ff *firstRowFunction) CalculateDefaultValue(schema *expression.Schema, ctx context.Context) (d types.Datum, valid bool) {
arg := ff.Args[0]
result, err := expression.EvaluateExprWithNull(ctx, schema, arg)
if err != nil {
log.Warnf("Evaluate expr with null failed in function %s, err msg is %s", ff, err.Error())
return d, false
}
if con, ok := result.(*expression.Constant); ok {
return con.Value, true
}
return d, false
}