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merge_sort.go
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merge_sort.go
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/*
Copyright 2019 The Vitess Authors.
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 planbuilder
import (
"vitess.io/vitess/go/sqltypes"
"vitess.io/vitess/go/vt/vtgate/engine"
"vitess.io/vitess/go/vt/vtgate/semantics"
)
var _ logicalPlan = (*mergeSort)(nil)
// mergeSort is a pseudo-primitive. It amends the
// the underlying Route to perform a merge sort.
// It's differentiated as a separate primitive
// because some operations cannot be pushed down,
// which would otherwise be possible with a simple route.
// Since ORDER BY happens near the end of the SQL processing,
// most functions of this primitive are unreachable.
type mergeSort struct {
resultsBuilder
truncateColumnCount int
}
// newMergeSort builds a new mergeSort.
func newMergeSort(rb *route) *mergeSort {
ms := &mergeSort{
resultsBuilder: newResultsBuilder(rb, nil),
}
ms.truncater = ms
return ms
}
// SetTruncateColumnCount satisfies the truncater interface.
// This function records the truncate column count and sets
// it later on the eroute during wire-up phase.
func (ms *mergeSort) SetTruncateColumnCount(count int) {
ms.truncateColumnCount = count
}
// Primitive implements the logicalPlan interface
func (ms *mergeSort) Primitive() engine.Primitive {
return ms.input.Primitive()
}
// Wireup implements the logicalPlan interface
func (ms *mergeSort) Wireup(plan logicalPlan, jt *jointab) error {
// If the route has to do the ordering, and if any columns are Text,
// we have to request the corresponding weight_string from mysql
// and use that value instead. This is because we cannot mimic
// mysql's collation behavior yet.
rb := ms.input.(*route)
for i, orderby := range rb.eroute.OrderBy {
rc := ms.resultColumns[orderby.Col]
// Add a weight_string column if we know that the column is a textual column or if its type is unknown
if sqltypes.IsText(rc.column.typ) || rc.column.typ == sqltypes.Null {
var err error
rb.eroute.OrderBy[i].WeightStringCol, err = rb.SupplyWeightString(orderby.Col, orderby.FromGroupBy)
if err != nil {
_, isUnsupportedErr := err.(UnsupportedSupplyWeightString)
if isUnsupportedErr {
continue
}
return err
}
ms.truncateColumnCount = len(ms.resultColumns)
}
}
rb.eroute.TruncateColumnCount = ms.truncateColumnCount
return ms.input.Wireup(plan, jt)
}
func (ms *mergeSort) WireupGen4(semTable *semantics.SemTable) error {
return ms.input.WireupGen4(semTable)
}