/
last.go
executable file
·108 lines (88 loc) · 2.79 KB
/
last.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"
"github.com/Rock-liyi/p2pdb-store/sql"
"github.com/Rock-liyi/p2pdb-store/sql/expression"
)
// Last aggregation returns the last of all values in the selected column.
// It implements the Aggregation interface.
type Last struct {
expression.UnaryExpression
}
var _ sql.FunctionExpression = (*Last)(nil)
var _ sql.Aggregation = (*Last)(nil)
// NewLast returns a new Last node.
func NewLast(e sql.Expression) *Last {
return &Last{expression.UnaryExpression{Child: e}}
}
// FunctionName implements sql.FunctionExpression
func (l *Last) FunctionName() string {
return "last"
}
// Description implements sql.FunctionExpression
func (l *Last) Description() string {
return "returns the last value in a sequence of elements of an aggregation."
}
// Type returns the resultant type of the aggregation.
func (l *Last) Type() sql.Type {
return l.Child.Type()
}
func (l *Last) String() string {
return fmt.Sprintf("LAST(%s)", l.Child)
}
// WithChildren implements the sql.Expression interface.
func (l *Last) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(l, len(children), 1)
}
return NewLast(children[0]), nil
}
// NewBuffer creates a new buffer to compute the result.
func (l *Last) NewBuffer() (sql.AggregationBuffer, error) {
bufferChild, err := expression.Clone(l.UnaryExpression.Child)
if err != nil {
return nil, err
}
return &lastBuffer{nil, bufferChild}, nil
}
// Eval implements the sql.Expression interface.
func (l *Last) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
return nil, ErrEvalUnsupportedOnAggregation.New("Last")
}
type lastBuffer struct {
val interface{}
expr sql.Expression
}
// Update implements the AggregationBuffer interface.
func (l *lastBuffer) Update(ctx *sql.Context, row sql.Row) error {
v, err := l.expr.Eval(ctx, row)
if err != nil {
return err
}
if v == nil {
return nil
}
l.val = v
return nil
}
// Eval implements the AggregationBuffer interface.
func (l *lastBuffer) Eval(ctx *sql.Context) (interface{}, error) {
return l.val, nil
}
// Dispose implements the Disposable interface.
func (l *lastBuffer) Dispose() {
expression.Dispose(l.expr)
}