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topn.go
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topn.go
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// Copyright 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 analyzer
import (
"github.com/gabereiser/go-mysql-server/sql"
"github.com/gabereiser/go-mysql-server/sql/expression"
"github.com/gabereiser/go-mysql-server/sql/plan"
"github.com/gabereiser/go-mysql-server/sql/transform"
)
// insertTopNNodes replaces Limit(Sort(...)) and Limit(Offset(Sort(...))) with
// a TopN node.
func insertTopNNodes(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope, sel RuleSelector) (sql.Node, transform.TreeIdentity, error) {
var updateCalcFoundRows bool
return transform.NodeWithCtx(n, nil, func(tc transform.Context) (sql.Node, transform.TreeIdentity, error) {
if o, ok := tc.Node.(*plan.Offset); ok {
parentLimit, ok := tc.Parent.(*plan.Limit)
if !ok {
return tc.Node, transform.SameTree, nil
}
childSort, ok := o.UnaryNode.Child.(*plan.Sort)
if !ok {
return tc.Node, transform.SameTree, nil
}
topn := plan.NewTopN(childSort.SortFields, expression.NewPlus(parentLimit.Limit, o.Offset), childSort.UnaryNode.Child)
topn = topn.WithCalcFoundRows(parentLimit.CalcFoundRows)
updateCalcFoundRows = true
node, err := o.WithChildren(topn)
return node, transform.NewTree, err
} else if l, ok := tc.Node.(*plan.Limit); ok {
childSort, ok := l.UnaryNode.Child.(*plan.Sort)
if !ok {
if updateCalcFoundRows {
updateCalcFoundRows = false
return l.WithCalcFoundRows(false), transform.NewTree, nil
}
return tc.Node, transform.SameTree, nil
}
topn := plan.NewTopN(childSort.SortFields, l.Limit, childSort.UnaryNode.Child)
topn = topn.WithCalcFoundRows(l.CalcFoundRows)
node, err := l.WithCalcFoundRows(false).WithChildren(topn)
return node, transform.NewTree, err
}
return tc.Node, transform.SameTree, nil
})
}