/
min.go
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/
min.go
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// Copyright 2020-2021 Dolthub, 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package aggregation
import (
"fmt"
"reflect"
"github.com/Ciyfly/FakerMysql/sql"
"github.com/Ciyfly/FakerMysql/sql/expression"
)
// Min aggregation returns the smallest value of the selected column.
// It implements the Aggregation interface
type Min struct {
expression.UnaryExpression
}
var _ sql.FunctionExpression = (*Min)(nil)
var _ sql.Aggregation = (*Min)(nil)
// NewMin creates a new Min node.
func NewMin(e sql.Expression) *Min {
return &Min{expression.UnaryExpression{Child: e}}
}
// FunctionName implements sql.FunctionExpression
func (m *Min) FunctionName() string {
return "min"
}
// Type returns the resultant type of the aggregation.
func (m *Min) Type() sql.Type {
return m.Child.Type()
}
func (m *Min) String() string {
return fmt.Sprintf("MIN(%s)", m.Child)
}
// IsNullable returns whether the return value can be null.
func (m *Min) IsNullable() bool {
return true
}
// WithChildren implements the Expression interface.
func (m *Min) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(m, len(children), 1)
}
return NewMin(children[0]), nil
}
// NewBuffer creates a new buffer to compute the result.
func (m *Min) NewBuffer() (sql.AggregationBuffer, error) {
bufferChild, err := expression.Clone(m.UnaryExpression.Child)
if err != nil {
return nil, err
}
return &minBuffer{nil, bufferChild}, nil
}
// Eval implements the Expression interface.
func (m *Min) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
return nil, ErrEvalUnsupportedOnAggregation.New("Min")
}
type minBuffer struct {
val interface{}
expr sql.Expression
}
// Update implements the AggregationBuffer interface.
func (m *minBuffer) Update(ctx *sql.Context, row sql.Row) error {
v, err := m.expr.Eval(ctx, row)
if err != nil {
return err
}
if reflect.TypeOf(v) == nil {
return nil
}
if m.val == nil {
m.val = v
return nil
}
cmp, err := m.expr.Type().Compare(v, m.val)
if err != nil {
return err
}
if cmp == -1 {
m.val = v
}
return nil
}
// Eval implements the AggregationBuffer interface.
func (m *minBuffer) Eval(ctx *sql.Context) (interface{}, error) {
return m.val, nil
}
// Dispose implements the Disposable interface.
func (m *minBuffer) Dispose() {
expression.Dispose(m.expr)
}