/
limit.go
185 lines (160 loc) · 4.38 KB
/
limit.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 plan
import (
"fmt"
"io"
opentracing "github.com/opentracing/opentracing-go"
"github.com/Ciyfly/FakerMysql/sql"
)
// Limit is a node that only allows up to N rows to be retrieved.
type Limit struct {
UnaryNode
Limit sql.Expression
CalcFoundRows bool
}
// NewLimit creates a new Limit node with the given size.
func NewLimit(size sql.Expression, child sql.Node) *Limit {
return &Limit{
UnaryNode: UnaryNode{Child: child},
Limit: size,
}
}
// Expressions implements sql.Expressioner
func (l *Limit) Expressions() []sql.Expression {
return []sql.Expression{l.Limit}
}
// WithExpressions implements sql.Expressioner
func (l Limit) WithExpressions(exprs ...sql.Expression) (sql.Node, error) {
if len(exprs) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(l, len(exprs), 1)
}
nl := &l
nl.Limit = exprs[0]
return nl, nil
}
// Resolved implements the Resolvable interface.
func (l *Limit) Resolved() bool {
return l.UnaryNode.Child.Resolved() && l.Limit.Resolved()
}
// RowIter implements the Node interface.
func (l *Limit) RowIter(ctx *sql.Context, row sql.Row) (sql.RowIter, error) {
span, ctx := ctx.Span("plan.Limit", opentracing.Tag{Key: "limit", Value: l.Limit})
limit, err := getInt64Value(ctx, l.Limit)
if err != nil {
return nil, err
}
childIter, err := l.Child.RowIter(ctx, row)
if err != nil {
span.Finish()
return nil, err
}
return sql.NewSpanIter(span, &limitIter{
l: l,
limit: limit,
childIter: childIter,
}), nil
}
// getInt64Value returns the int64 literal value in the expression given, or an error with the errStr given if it
// cannot.
func getInt64Value(ctx *sql.Context, expr sql.Expression) (int64, error) {
i, err := expr.Eval(ctx, nil)
if err != nil {
return 0, err
}
switch i := i.(type) {
case int:
return int64(i), nil
case int8:
return int64(i), nil
case int16:
return int64(i), nil
case int32:
return int64(i), nil
case int64:
return i, nil
case uint:
return int64(i), nil
case uint8:
return int64(i), nil
case uint16:
return int64(i), nil
case uint32:
return int64(i), nil
case uint64:
return int64(i), nil
default:
// analyzer should catch this already
panic(fmt.Sprintf("Unsupported type for limit %T", i))
}
}
// WithChildren implements the Node interface.
func (l *Limit) WithChildren(children ...sql.Node) (sql.Node, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(l, len(children), 1)
}
nl := *l
nl.Child = children[0]
return &nl, nil
}
func (l Limit) String() string {
pr := sql.NewTreePrinter()
_ = pr.WriteNode("Limit(%s)", l.Limit)
_ = pr.WriteChildren(l.Child.String())
return pr.String()
}
func (l Limit) DebugString() string {
pr := sql.NewTreePrinter()
_ = pr.WriteNode("Limit(%s)", l.Limit)
_ = pr.WriteChildren(sql.DebugString(l.Child))
return pr.String()
}
type limitIter struct {
l *Limit
currentPos int64
childIter sql.RowIter
limit int64
}
func (li *limitIter) Next() (sql.Row, error) {
if li.currentPos >= li.limit {
// If we were asked to calc all found rows, then when we are past the limit we iterate over the rest of the
// result set to count it
if li.l.CalcFoundRows {
for {
_, err := li.childIter.Next()
if err != nil {
return nil, err
}
li.currentPos++
}
}
return nil, io.EOF
}
childRow, err := li.childIter.Next()
li.currentPos++
if err != nil {
return nil, err
}
return childRow, nil
}
func (li *limitIter) Close(ctx *sql.Context) error {
err := li.childIter.Close(ctx)
if err != nil {
return err
}
if li.l.CalcFoundRows {
ctx.SetLastQueryInfo(sql.FoundRows, li.currentPos)
}
return nil
}