Adding the challenge 0301

0301/assert.go

@@ -0,0 +1,9 @@
+package db0301
+
+func check(cond bool) {
+	if !cond {
+		panic("assertion failure")
+	}
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/cell.go

@@ -0,0 +1,57 @@
+package db0301
+
+import (
+	"encoding/binary"
+	"errors"
+	"slices"
+)
+
+type CellType uint8
+
+const (
+	TypeI64 CellType = 1
+	TypeStr CellType = 2
+)
+
+type Cell struct {
+	Type CellType
+	I64  int64
+	Str  []byte
+}
+
+func (cell *Cell) Encode(toAppend []byte) []byte {
+	switch cell.Type {
+	case TypeI64:
+		return binary.LittleEndian.AppendUint64(toAppend, uint64(cell.I64))
+	case TypeStr:
+		toAppend = binary.LittleEndian.AppendUint32(toAppend, uint32(len(cell.Str)))
+		return append(toAppend, cell.Str...)
+	default:
+		panic("unreachable")
+	}
+}
+
+func (cell *Cell) Decode(data []byte) (rest []byte, err error) {
+	switch cell.Type {
+	case TypeI64:
+		if len(data) < 8 {
+			return data, errors.New("expect more data")
+		}
+		cell.I64 = int64(binary.LittleEndian.Uint64(data[0:8]))
+		return data[8:], nil
+	case TypeStr:
+		if len(data) < 4 {
+			return data, errors.New("expect more data")
+		}
+		size := int(binary.LittleEndian.Uint32(data[0:4]))
+		if len(data) < 4+size {
+			return data, errors.New("expect more data")
+		}
+		cell.Str = slices.Clone(data[4 : 4+size])
+		return data[4+size:], nil
+	default:
+		panic("unreachable")
+	}
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/cell_test.go

@@ -0,0 +1,27 @@
+package db0301
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTableCell(t *testing.T) {
+	cell := Cell{Type: TypeI64, I64: -2}
+	data := []byte{0xfe, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
+	assert.Equal(t, data, cell.Encode(nil))
+	decoded := Cell{Type: TypeI64}
+	rest, err := decoded.Decode(data)
+	assert.True(t, len(rest) == 0 && err == nil)
+	assert.Equal(t, cell, decoded)
+
+	cell = Cell{Type: TypeStr, Str: []byte("asdf")}
+	data = []byte{4, 0, 0, 0, 'a', 's', 'd', 'f'}
+	assert.Equal(t, data, cell.Encode(nil))
+	decoded = Cell{Type: TypeStr}
+	rest, err = decoded.Decode(data)
+	assert.True(t, len(rest) == 0 && err == nil)
+	assert.Equal(t, cell, decoded)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/kv.go

@@ -0,0 +1,87 @@
+package db0301
+
+import (
+	"bytes"
+)
+
+type KV struct {
+	log Log
+	mem map[string][]byte
+}
+
+func (kv *KV) Open() error {
+	if err := kv.log.Open(); err != nil {
+		return err
+	}
+
+	kv.mem = map[string][]byte{}
+	for {
+		ent := Entry{}
+		eof, err := kv.log.Read(&ent)
+		if err != nil {
+			return err
+		} else if eof {
+			break
+		}
+
+		if ent.deleted {
+			delete(kv.mem, string(ent.key))
+		} else {
+			kv.mem[string(ent.key)] = ent.val
+		}
+	}
+	return nil
+}
+
+func (kv *KV) Close() error { return kv.log.Close() }
+
+func (kv *KV) Get(key []byte) (val []byte, ok bool, err error) {
+	val, ok = kv.mem[string(key)]
+	return
+}
+
+type UpdateMode int
+
+const (
+	ModeUpsert UpdateMode = 0 // insert or update
+	ModeInsert UpdateMode = 1 // insert new
+	ModeUpdate UpdateMode = 2 // update existing
+)
+
+func (kv *KV) SetEx(key []byte, val []byte, mode UpdateMode) (updated bool, err error) {
+	prev, exist := kv.mem[string(key)]
+	switch mode {
+	case ModeUpsert:
+		updated = !exist || !bytes.Equal(prev, val)
+	case ModeInsert:
+		updated = !exist
+	case ModeUpdate:
+		updated = exist && !bytes.Equal(prev, val)
+	default:
+		panic("unreachable")
+	}
+	if updated {
+		if err = kv.log.Write(&Entry{key: key, val: val}); err != nil {
+			return false, err
+		}
+		kv.mem[string(key)] = val
+	}
+	return
+}
+
+func (kv *KV) Set(key []byte, val []byte) (updated bool, err error) {
+	return kv.SetEx(key, val, ModeUpsert)
+}
+
+func (kv *KV) Del(key []byte) (deleted bool, err error) {
+	_, deleted = kv.mem[string(key)]
+	if deleted {
+		if err = kv.log.Write(&Entry{key: key, deleted: true}); err != nil {
+			return false, err
+		}
+		delete(kv.mem, string(key))
+	}
+	return
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/kv_entry.go

@@ -0,0 +1,63 @@
+package db0301
+
+import (
+	"encoding/binary"
+	"errors"
+	"hash/crc32"
+	"io"
+)
+
+type Entry struct {
+	key     []byte
+	val     []byte
+	deleted bool
+}
+
+func (ent *Entry) Encode() []byte {
+	data := make([]byte, 4+4+4+1+len(ent.key)+len(ent.val))
+	binary.LittleEndian.PutUint32(data[4:8], uint32(len(ent.key)))
+	copy(data[4+4+4+1:], ent.key)
+	if ent.deleted {
+		data[4+4+4] = 1
+	} else {
+		binary.LittleEndian.PutUint32(data[8:12], uint32(len(ent.val)))
+		copy(data[4+4+4+1+len(ent.key):], ent.val)
+	}
+	binary.LittleEndian.PutUint32(data[0:4], crc32.ChecksumIEEE(data[4:]))
+	return data
+}
+
+var ErrBadSum = errors.New("bad checksum")
+
+func (ent *Entry) Decode(r io.Reader) error {
+	var header [4 + 4 + 4 + 1]byte
+	if _, err := io.ReadFull(r, header[:]); err != nil {
+		return err
+	}
+	klen := int(binary.LittleEndian.Uint32(header[4:8]))
+	vlen := int(binary.LittleEndian.Uint32(header[8:12]))
+	deleted := header[4+4+4]
+
+	data := make([]byte, klen+vlen)
+	if _, err := io.ReadFull(r, data); err != nil {
+		return err
+	}
+
+	h := crc32.NewIEEE()
+	h.Write(header[4:])
+	h.Write(data)
+	if h.Sum32() != binary.LittleEndian.Uint32(header[0:4]) {
+		return ErrBadSum
+	}
+
+	ent.key = data[:klen]
+	if deleted != 0 {
+		ent.deleted = true
+	} else {
+		ent.deleted = false
+		ent.val = data[klen:]
+	}
+	return nil
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/kv_test.go

@@ -0,0 +1,158 @@
+package db0301
+
+import (
+	"bytes"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestKVBasic(t *testing.T) {
+	kv := KV{}
+	kv.log.FileName = ".test_db"
+	defer os.Remove(kv.log.FileName)
+
+	os.Remove(kv.log.FileName)
+	err := kv.Open()
+	assert.Nil(t, err)
+	defer kv.Close()
+
+	updated, err := kv.Set([]byte("k1"), []byte("v1"))
+	assert.True(t, updated && err == nil)
+
+	val, ok, err := kv.Get([]byte("k1"))
+	assert.True(t, string(val) == "v1" && ok && err == nil)
+
+	_, ok, err = kv.Get([]byte("xxx"))
+	assert.True(t, !ok && err == nil)
+
+	updated, err = kv.Del([]byte("xxx"))
+	assert.True(t, !updated && err == nil)
+
+	updated, err = kv.Del([]byte("k1"))
+	assert.True(t, updated && err == nil)
+
+	_, ok, err = kv.Get([]byte("xxx"))
+	assert.True(t, !ok && err == nil)
+
+	updated, err = kv.Set([]byte("k2"), []byte("v2"))
+	assert.True(t, updated && err == nil)
+
+	// reopen
+	kv.Close()
+	err = kv.Open()
+	assert.Nil(t, err)
+
+	_, ok, err = kv.Get([]byte("k1"))
+	assert.True(t, !ok && err == nil)
+	val, ok, err = kv.Get([]byte("k2"))
+	assert.True(t, string(val) == "v2" && ok && err == nil)
+}
+
+func TestKVUpdateMode(t *testing.T) {
+	kv := KV{}
+	kv.log.FileName = ".test_db"
+	defer os.Remove(kv.log.FileName)
+
+	os.Remove(kv.log.FileName)
+	err := kv.Open()
+	assert.Nil(t, err)
+	defer kv.Close()
+
+	updated, err := kv.SetEx([]byte("k1"), []byte("v1"), ModeUpdate)
+	assert.True(t, !updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k1"), []byte("v1"), ModeUpdate)
+	assert.True(t, !updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k1"), []byte("v1"), ModeInsert)
+	assert.True(t, updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k1"), []byte("xx"), ModeInsert)
+	assert.True(t, !updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k1"), []byte("yy"), ModeUpdate)
+	assert.True(t, updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k1"), []byte("zz"), ModeUpsert)
+	assert.True(t, updated && err == nil)
+
+	updated, err = kv.SetEx([]byte("k2"), []byte("tt"), ModeUpsert)
+	assert.True(t, updated && err == nil)
+}
+
+func TestKVRecovery(t *testing.T) {
+	kv := KV{}
+	kv.log.FileName = ".test_db"
+	defer os.Remove(kv.log.FileName)
+
+	prepare := func() {
+		os.Remove(kv.log.FileName)
+
+		err := kv.Open()
+		assert.Nil(t, err)
+		defer kv.Close()
+
+		updated, err := kv.Set([]byte("k1"), []byte("v1"))
+		assert.True(t, updated && err == nil)
+		updated, err = kv.Set([]byte("k2"), []byte("v2"))
+		assert.True(t, updated && err == nil)
+	}
+
+	prepare()
+	// simulate truncated log
+	fp, _ := os.OpenFile(kv.log.FileName, os.O_RDWR, 0o644)
+	st, _ := fp.Stat()
+	fp.Truncate(st.Size() - 1)
+	fp.Close()
+	// reopen
+	err := kv.Open()
+	assert.Nil(t, err)
+	// test
+	val, ok, err := kv.Get([]byte("k1"))
+	assert.True(t, string(val) == "v1" && ok && err == nil)
+	_, ok, err = kv.Get([]byte("k2")) // bad
+	assert.True(t, !ok && err == nil)
+	kv.Close()
+
+	prepare()
+	// simulate bad checksum
+	fp, _ = os.OpenFile(kv.log.FileName, os.O_RDWR, 0o644)
+	st, _ = fp.Stat()
+	fp.WriteAt([]byte{0}, st.Size()-1)
+	fp.Close()
+	// reopen
+	err = kv.Open()
+	assert.Nil(t, err)
+	// test
+	val, ok, err = kv.Get([]byte("k1"))
+	assert.True(t, string(val) == "v1" && ok && err == nil)
+	_, ok, err = kv.Get([]byte("k2")) // bad
+	assert.True(t, !ok && err == nil)
+	kv.Close()
+}
+
+func TestEntryEncode(t *testing.T) {
+	ent := Entry{key: []byte("k1"), val: []byte("xxx")}
+	data := []byte{0xe9, 0xec, 0x4d, 0x9e, 2, 0, 0, 0, 3, 0, 0, 0, 0, 'k', '1', 'x', 'x', 'x'}
+
+	assert.Equal(t, data, ent.Encode())
+
+	decoded := Entry{}
+	err := decoded.Decode(bytes.NewBuffer(data))
+	assert.Nil(t, err)
+	assert.Equal(t, ent, decoded)
+
+	ent = Entry{key: []byte("k1"), deleted: true}
+	data = []byte{0x4c, 0xd0, 0xfe, 0xe5, 2, 0, 0, 0, 0, 0, 0, 0, 1, 'k', '1'}
+
+	assert.Equal(t, data, ent.Encode())
+
+	decoded = Entry{}
+	err = decoded.Decode(bytes.NewBuffer(data))
+	assert.Nil(t, err)
+	assert.Equal(t, ent, decoded)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/log.go

@@ -0,0 +1,40 @@
+package db0301
+
+import (
+	"io"
+	"os"
+)
+
+type Log struct {
+	FileName string
+	fp       *os.File
+}
+
+func (log *Log) Open() (err error) {
+	log.fp, err = createFileSync(log.FileName)
+	return err
+}
+
+func (log *Log) Close() error {
+	return log.fp.Close()
+}
+
+func (log *Log) Write(ent *Entry) error {
+	if _, err := log.fp.Write(ent.Encode()); err != nil {
+		return err
+	}
+	return log.fp.Sync() // fsync
+}
+
+func (log *Log) Read(ent *Entry) (eof bool, err error) {
+	err = ent.Decode(log.fp)
+	if err == io.EOF || err == io.ErrUnexpectedEOF || err == ErrBadSum {
+		return true, nil
+	} else if err != nil {
+		return false, err
+	} else {
+		return false, nil
+	}
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/os_other.go

@@ -0,0 +1,11 @@
+//go:build !unix
+
+package db0301
+
+import "os"
+
+func createFileSync(file string) (*os.File, error) {
+	return os.OpenFile(file, os.O_RDWR|os.O_CREATE, 0o644)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/os_unix.go

@@ -0,0 +1,34 @@
+//go:build unix
+
+package db0301
+
+import (
+	"os"
+	"path"
+	"syscall"
+)
+
+// open or create a file and fsync the directory
+func createFileSync(file string) (*os.File, error) {
+	fp, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE, 0o644)
+	if err != nil {
+		return nil, err
+	}
+	if err = syncDir(path.Base(file)); err != nil {
+		_ = fp.Close()
+		return nil, err
+	}
+	return fp, err
+}
+
+func syncDir(file string) error {
+	flags := os.O_RDONLY | syscall.O_DIRECTORY
+	dirfd, err := syscall.Open(path.Dir(file), flags, 0o644)
+	if err != nil {
+		return err
+	}
+	defer syscall.Close(dirfd)
+	return syscall.Fsync(dirfd)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/row.go

@@ -0,0 +1,95 @@
+package db0301
+
+import (
+	"errors"
+	"slices"
+)
+
+type Schema struct {
+	Table string
+	Cols  []Column
+	PKey  []int // indexes of primary key columns
+}
+
+type Column struct {
+	Name string
+	Type CellType
+}
+
+type Row []Cell
+
+func (schema *Schema) NewRow() Row {
+	return make(Row, len(schema.Cols))
+}
+
+func (row Row) EncodeKey(schema *Schema) (key []byte) {
+	key = append(key, []byte(schema.Table)...)
+	key = append(key, 0x00)
+	check(len(row) == len(schema.Cols))
+	for idx, value := range row {
+		if slices.Contains(schema.PKey, idx) {
+			check(value.Type == schema.Cols[idx].Type)
+			key = row[idx].Encode(key)
+		}
+	}
+	return key
+}
+
+func (row Row) EncodeVal(schema *Schema) (val []byte) {
+	check(len(row) == len(schema.Cols))
+	for idx, value := range row {
+		if !slices.Contains(schema.PKey, idx) {
+			check(value.Type == schema.Cols[idx].Type)
+			val = row[idx].Encode(val)
+		}
+	}
+	return val
+}
+
+func (row Row) DecodeKey(schema *Schema, key []byte) (err error) {
+	check(len(row) == len(schema.Cols))
+
+	if len(key) < len(schema.Table)+1 {
+		return errors.New("bad key")
+	}
+	if string(key[:len(schema.Table)+1]) != schema.Table+"\x00" {
+		return errors.New("bad key")
+	}
+	key = key[len(schema.Table)+1:]
+
+	for idx, col := range schema.Cols {
+		if !slices.Contains(schema.PKey, idx) {
+			continue
+		}
+		row[idx] = Cell{Type: col.Type}
+		if key, err = row[idx].Decode(key); err != nil {
+			return err
+		}
+	}
+
+	if len(key) != 0 {
+		return errors.New("trailing garbage")
+	}
+	return nil
+}
+
+func (row Row) DecodeVal(schema *Schema, val []byte) (err error) {
+	check(len(row) == len(schema.Cols))
+
+	for idx, col := range schema.Cols {
+		if slices.Contains(schema.PKey, idx) {
+			continue
+		}
+		row[idx] = Cell{Type: col.Type}
+		if val, err = row[idx].Decode(val); err != nil {
+			return err
+		}
+	}
+
+	if len(val) != 0 {
+		return errors.New("trailing garbage")
+	}
+	return nil
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/row_test.go

@@ -0,0 +1,38 @@
+package db0301
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRowEncode(t *testing.T) {
+	schema := &Schema{
+		Table: "link",
+		Cols: []Column{
+			{Name: "time", Type: TypeI64},
+			{Name: "src", Type: TypeStr},
+			{Name: "dst", Type: TypeStr},
+		},
+		PKey: []int{1, 2}, // (src, dst)
+	}
+
+	row := Row{
+		Cell{Type: TypeI64, I64: 123},
+		Cell{Type: TypeStr, Str: []byte("a")},
+		Cell{Type: TypeStr, Str: []byte("b")},
+	}
+	key := []byte{'l', 'i', 'n', 'k', 0, 1, 0, 0, 0, 'a', 1, 0, 0, 0, 'b'}
+	val := []byte{123, 0, 0, 0, 0, 0, 0, 0}
+	assert.Equal(t, key, row.EncodeKey(schema))
+	assert.Equal(t, val, row.EncodeVal(schema))
+
+	decoded := schema.NewRow()
+	err := decoded.DecodeKey(schema, key)
+	assert.Nil(t, err)
+	err = decoded.DecodeVal(schema, val)
+	assert.Nil(t, err)
+	assert.Equal(t, row, decoded)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/sql_parser.go

@@ -0,0 +1,50 @@
+package db0301
+
+type Parser struct {
+	buf string
+	pos int
+}
+
+func NewParser(s string) Parser {
+	return Parser{buf: s, pos: 0}
+}
+
+func isSpace(ch byte) bool {
+	switch ch {
+	case '\t', '\n', '\v', '\f', '\r', ' ':
+		return true
+	}
+	return false
+}
+func isAlpha(ch byte) bool {
+	return 'a' <= (ch|32) && (ch|32) <= 'z'
+}
+func isDigit(ch byte) bool {
+	return '0' <= ch && ch <= '9'
+}
+func isNameStart(ch byte) bool {
+	return isAlpha(ch) || ch == '_'
+}
+func isNameContinue(ch byte) bool {
+	return isAlpha(ch) || isDigit(ch) || ch == '_'
+}
+func isSeparator(ch byte) bool {
+	return ch < 128 && !isNameContinue(ch)
+}
+
+func (p *Parser) skipSpaces() {
+	for p.pos < len(p.buf) && isSpace(p.buf[p.pos]) {
+		p.pos += 1
+	}
+}
+
+func (p *Parser) tryKeyword(kw string) bool
+
+func (p *Parser) tryName() (string, bool)
+
+func (p *Parser) isEnd() bool {
+	p.skipSpaces()
+	return p.pos >= len(p.buf)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/sql_parser_test.go

@@ -0,0 +1,28 @@
+package db0301
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseName(t *testing.T) {
+	p := NewParser(" a b0 _0_ 123 ")
+	name, ok := p.tryName()
+	assert.True(t, ok && name == "a")
+	name, ok = p.tryName()
+	assert.True(t, ok && name == "b0")
+	name, ok = p.tryName()
+	assert.True(t, ok && name == "_0_")
+	_, ok = p.tryName()
+	assert.False(t, ok)
+}
+
+func TestParseKeyword(t *testing.T) {
+	p := NewParser(" select  HELLO ")
+	assert.False(t, p.tryKeyword("sel"))
+	assert.True(t, p.tryKeyword("SELECT"))
+	assert.True(t, p.tryKeyword("hello") && p.isEnd())
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/table.go

@@ -0,0 +1,45 @@
+package db0301
+
+type DB struct {
+	KV KV
+}
+
+func (db *DB) Open() error  { return db.KV.Open() }
+func (db *DB) Close() error { return db.KV.Close() }
+
+func (db *DB) Select(schema *Schema, row Row) (ok bool, err error) {
+	key := row.EncodeKey(schema)
+	val, ok, err := db.KV.Get(key)
+	if err != nil || !ok {
+		return ok, err
+	}
+	if err = row.DecodeVal(schema, val); err != nil {
+		return false, err
+	}
+	return true, nil
+}
+
+func (db *DB) Insert(schema *Schema, row Row) (updated bool, err error) {
+	key := row.EncodeKey(schema)
+	val := row.EncodeVal(schema)
+	return db.KV.SetEx(key, val, ModeInsert)
+}
+
+func (db *DB) Upsert(schema *Schema, row Row) (updated bool, err error) {
+	key := row.EncodeKey(schema)
+	val := row.EncodeVal(schema)
+	return db.KV.SetEx(key, val, ModeUpsert)
+}
+
+func (db *DB) Update(schema *Schema, row Row) (updated bool, err error) {
+	key := row.EncodeKey(schema)
+	val := row.EncodeVal(schema)
+	return db.KV.SetEx(key, val, ModeUpdate)
+}
+
+func (db *DB) Delete(schema *Schema, row Row) (deleted bool, err error) {
+	key := row.EncodeKey(schema)
+	return db.KV.Del(key)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/

0301/table_test.go

@@ -0,0 +1,65 @@
+package db0301
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTableByPKey(t *testing.T) {
+	db := DB{}
+	db.KV.log.FileName = ".test_db"
+	defer os.Remove(db.KV.log.FileName)
+
+	os.Remove(db.KV.log.FileName)
+	err := db.Open()
+	assert.Nil(t, err)
+	defer db.Close()
+
+	schema := &Schema{
+		Table: "link",
+		Cols: []Column{
+			{Name: "time", Type: TypeI64},
+			{Name: "src", Type: TypeStr},
+			{Name: "dst", Type: TypeStr},
+		},
+		PKey: []int{1, 2}, // (src, dst)
+	}
+
+	row := Row{
+		Cell{Type: TypeI64, I64: 123},
+		Cell{Type: TypeStr, Str: []byte("a")},
+		Cell{Type: TypeStr, Str: []byte("b")},
+	}
+	ok, err := db.Select(schema, row)
+	assert.True(t, !ok && err == nil)
+
+	updated, err := db.Insert(schema, row)
+	assert.True(t, updated && err == nil)
+
+	out := Row{
+		Cell{},
+		Cell{Type: TypeStr, Str: []byte("a")},
+		Cell{Type: TypeStr, Str: []byte("b")},
+	}
+	ok, err = db.Select(schema, out)
+	assert.True(t, ok && err == nil)
+	assert.Equal(t, row, out)
+
+	row[0].I64 = 456
+	updated, err = db.Update(schema, row)
+	assert.True(t, updated && err == nil)
+
+	ok, err = db.Select(schema, out)
+	assert.True(t, ok && err == nil)
+	assert.Equal(t, row, out)
+
+	deleted, err := db.Delete(schema, row)
+	assert.True(t, deleted && err == nil)
+
+	ok, err = db.Select(schema, row)
+	assert.True(t, !ok && err == nil)
+}
+
+// QzBQWVJJOUhU https://trialofcode.org/