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select.go
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select.go
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package planner
import (
"fmt"
"go/token"
"go/types"
"strings"
"github.com/auxten/go-sqldb/node"
"github.com/auxten/go-sqldb/page"
"github.com/auxten/go-sqldb/parser"
"github.com/auxten/go-sqldb/utils"
)
func (plan *Plan) SelectPrepare(ast *parser.SelectTree) (filteredPipe chan *node.Row, err error) {
var (
table = plan.table
p *page.Page
)
// Get the start of table
if plan.cursor, err = table.Seek(0); err != nil {
return
}
if p, err = table.Pager.GetPage(plan.cursor.PageIdx); err != nil {
return
}
// If the key not found in the table and the page to insert that key
// has 0 cells. We got the end of the table.
plan.cursor.EndOfTable = p.LeafNode.Header.Cells == 0
/*
The code below demonstrates a simple "Volcano Model" query plan.
For more please refer to https://doi.org/10.1109/69.273032
*/
// Fetch rows from storage pages
go func(out chan<- *node.Row) {
var (
err error
row *node.Row
)
defer close(out)
for {
if row, err = plan.fetchRow(table); err != nil {
plan.ErrorsPipe <- err
return
}
select {
case <-plan.Stop:
return
case out <- row:
}
if plan.cursor.EndOfTable {
break
}
}
}(plan.UnFilteredPipe)
// Filter rows according the ast.Where
go func(in <-chan *node.Row, out chan<- *node.Row, where []string) {
defer close(out)
for row := range in {
if len(where) == 0 {
out <- row
continue
}
filtered, err := isRowFiltered(where, row)
if err != nil {
plan.ErrorsPipe <- err
return
}
if !filtered {
out <- row
}
}
}(plan.UnFilteredPipe, plan.FilteredPipe, ast.Where)
// Count row count for LIMIT clause.
go func(in <-chan *node.Row, out chan<- *node.Row, limit int64) {
defer close(out)
defer close(plan.Stop)
i := int64(0)
for row := range in {
i++
if i > limit && limit > 0 {
return
}
out <- row
}
}(plan.FilteredPipe, plan.LimitedPipe, ast.Limit)
return plan.LimitedPipe, nil
}
func (plan *Plan) fetchRow(table *page.Table) (row *node.Row, err error) {
var p *page.Page
if p, err = table.Pager.GetPage(plan.cursor.PageIdx); err != nil {
return
}
row = new(node.Row)
if _, err = row.Unmarshal(p.LeafNode.Cells[plan.cursor.CellIdx].Value[:]); err != nil {
row = nil
return
}
plan.cursor.CellIdx++
if plan.cursor.CellIdx >= p.LeafNode.Header.Cells {
// Move cursor to next leaf
if p.LeafNode.Header.NextLeaf == 0 {
// 已经移动到了最右的的叶子节点
plan.cursor.EndOfTable = true
} else {
plan.cursor.PageIdx = p.LeafNode.Header.NextLeaf
plan.cursor.CellIdx = 0
}
}
return
}
func isRowFiltered(where []string, row *node.Row) (filtered bool, err error) {
// This is a very dirty hack to use Eval to evaluate the Where statement.
var (
normalized = make([]string, len(where))
tv types.TypeAndValue
)
/*
type Row struct {
Id uint32
Sex byte
Age uint8
Username [32]byte
Email [128]byte
Phone [64]byte
}
*/
for i, w := range where {
upper := strings.ToUpper(w)
switch upper {
case "AND":
normalized[i] = "&&"
case "OR":
normalized[i] = "||"
case "ID":
normalized[i] = fmt.Sprintf("%d", row.Id)
case "SEX":
normalized[i] = fmt.Sprintf("%c", row.Sex)
case "AGE":
normalized[i] = fmt.Sprintf("%d", row.Age)
case "USERNAME":
normalized[i] = fmt.Sprintf("%s", string(row.Username[:utils.Length(row.Username[:])]))
case "EMAIL":
normalized[i] = fmt.Sprintf("%s", string(row.Email[:utils.Length(row.Email[:])]))
case "PHONE":
normalized[i] = fmt.Sprintf("%s", string(row.Phone[:utils.Length(row.Phone[:])]))
default:
normalized[i] = w
}
}
expr := strings.Join(normalized, " ")
fSet := token.NewFileSet()
if tv, err = types.Eval(fSet, nil, token.NoPos, expr); err != nil {
return
}
if tv.Type == nil {
err = fmt.Errorf("eval(%q) got nil type but no error", expr)
return
}
if !strings.Contains(tv.Type.String(), "bool") {
err = fmt.Errorf("eval(%q) got non bool type", expr)
return
}
if tv.Value.ExactString() == "true" {
filtered = false
} else {
filtered = true
}
return
}