forked from pingcap/tidb
/
max_min.go
93 lines (84 loc) · 2.54 KB
/
max_min.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
// 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 maxMinFunction struct {
aggFunction
isMax bool
}
// Clone implements Aggregation interface.
func (mmf *maxMinFunction) Clone() Aggregation {
nf := *mmf
for i, arg := range mmf.Args {
nf.Args[i] = arg.Clone()
}
return &nf
}
// CalculateDefaultValue implements Aggregation interface.
func (mmf *maxMinFunction) CalculateDefaultValue(schema *expression.Schema, ctx context.Context) (d types.Datum, valid bool) {
arg := mmf.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", mmf, err.Error())
return d, false
}
if con, ok := result.(*expression.Constant); ok {
return con.Value, true
}
return d, false
}
// GetType implements Aggregation interface.
func (mmf *maxMinFunction) GetType() *types.FieldType {
return mmf.Args[0].GetType()
}
// GetResult implements Aggregation interface.
func (mmf *maxMinFunction) GetResult(ctx *AggEvaluateContext) (d types.Datum) {
return ctx.Value
}
// GetPartialResult implements Aggregation interface.
func (mmf *maxMinFunction) GetPartialResult(ctx *AggEvaluateContext) []types.Datum {
return []types.Datum{mmf.GetResult(ctx)}
}
// Update implements Aggregation interface.
func (mmf *maxMinFunction) Update(ctx *AggEvaluateContext, sc *variable.StatementContext, row []types.Datum) error {
if len(mmf.Args) != 1 {
return errors.New("Wrong number of args for AggFuncMaxMin")
}
a := mmf.Args[0]
value, err := a.Eval(row)
if err != nil {
return errors.Trace(err)
}
if ctx.Value.IsNull() {
ctx.Value = value
}
if value.IsNull() {
return nil
}
var c int
c, err = ctx.Value.CompareDatum(sc, &value)
if err != nil {
return errors.Trace(err)
}
if (mmf.isMax && c == -1) || (!mmf.isMax && c == 1) {
ctx.Value = value
}
return nil
}