simple_projection.go

/*
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 (
	"fmt"

	"vitess.io/vitess/go/vt/sqlparser"
	"vitess.io/vitess/go/vt/vtgate/engine"
)

var _ logicalPlan = (*simpleProjection)(nil)

// simpleProjection is used for wrapping a derived table.
// This primitive wraps any derived table that results
// in something that's not a route. It builds a
// 'table' for the derived table allowing higher level
// constructs to reference its columns. If a derived table
// results in a route primitive, we instead build
// a new route that keeps the subquery in the FROM
// clause, because a route is more versatile than
// a simpleProjection.
// this should not be used by the gen4 planner
type simpleProjection struct {
	logicalPlanCommon
	resultColumns []*resultColumn
	eSimpleProj   *engine.SimpleProjection
}

// newSimpleProjection builds a new simpleProjection.
func newSimpleProjection(alias sqlparser.TableIdent, plan logicalPlan) (*simpleProjection, *symtab, error) {
	sq := &simpleProjection{
		logicalPlanCommon: newBuilderCommon(plan),
		eSimpleProj:       &engine.SimpleProjection{},
	}

	// Create a 'table' that represents the derived table.
	t := &table{
		alias:  sqlparser.TableName{Name: alias},
		origin: sq,
	}

	// Create column symbols based on the result column names.
	for _, rc := range plan.ResultColumns() {
		if _, ok := t.columns[rc.alias.Lowered()]; ok {
			return nil, nil, fmt.Errorf("duplicate column names in subquery: %s", sqlparser.String(rc.alias))
		}
		t.addColumn(rc.alias, &column{origin: sq})
	}
	t.isAuthoritative = true
	st := newSymtab()
	// AddTable will not fail because symtab is empty.
	_ = st.AddTable(t)
	return sq, st, nil
}

// Primitive implements the logicalPlan interface
func (sq *simpleProjection) Primitive() engine.Primitive {
	sq.eSimpleProj.Input = sq.input.Primitive()
	return sq.eSimpleProj
}

// ResultColumns implements the logicalPlan interface
func (sq *simpleProjection) ResultColumns() []*resultColumn {
	return sq.resultColumns
}

// SupplyCol implements the logicalPlan interface
func (sq *simpleProjection) SupplyCol(col *sqlparser.ColName) (rc *resultColumn, colNumber int) {
	c := col.Metadata.(*column)
	for i, rc := range sq.resultColumns {
		if rc.column == c {
			return rc, i
		}
	}

	// columns that reference subqueries will have their colNumber set.
	// Let's use it here.
	sq.eSimpleProj.Cols = append(sq.eSimpleProj.Cols, c.colNumber)
	sq.resultColumns = append(sq.resultColumns, &resultColumn{column: c})
	return rc, len(sq.resultColumns) - 1
}

// OutputColumns implements the logicalPlan interface
func (sq *simpleProjection) OutputColumns() []sqlparser.SelectExpr {
	exprs := make([]sqlparser.SelectExpr, 0, len(sq.eSimpleProj.Cols))
	outputCols := sq.input.OutputColumns()
	for _, colID := range sq.eSimpleProj.Cols {
		exprs = append(exprs, outputCols[colID])
	}
	return exprs
}