result.go

package ferndb

import (
	"errors"

	"github.com/chaitanya-uike/ferndb/attr"
	"github.com/chaitanya-uike/ferndb/catalog"
	"github.com/chaitanya-uike/ferndb/pipeline"
	"github.com/chaitanya-uike/ferndb/plan"
	"github.com/chaitanya-uike/ferndb/types"
)

type Result struct {
	Cols     []string
	Rows     [][]types.Value
	Affected int64
}

func (tx *Tx) resolveColumns(sp *plan.SelectPlan) ([]string, []attr.Attribute, error) {
	cat, err := tx.catalog()
	if err != nil {
		return nil, nil, err
	}
	names := make([]string, len(sp.OutputAttrs))
	for i, expr := range sp.Projections {
		names[i] = columnName(cat, expr)
	}
	return names, sp.OutputAttrs, nil
}

func columnName(cat *catalog.Catalog, expr plan.Expr) string {
	if c, ok := expr.(*plan.ColumnReference); ok {
		if s, ok := cat.Schema(c.Table); ok {
			if col := s.ColumnByID(c.ColumnID); col != nil {
				return col.Name
			}
		}
	}
	return "?column?"
}

func materialize(op pipeline.Op, attrs []attr.Attribute) ([][]types.Value, error) {
	if err := op.Open(); err != nil {
		return nil, err
	}
	defer op.Close()
	var out [][]types.Value
	for {
		row, err := op.Next()
		if errors.Is(err, pipeline.EOF) {
			return out, nil
		}
		if err != nil {
			return nil, err
		}
		values := make([]types.Value, len(attrs))
		for i, a := range attrs {
			values[i] = row[a]
		}
		out = append(out, values)
	}
}