func (s *selectStmt) explain(ctx *execCtx, w strutil.Formatter) {
	p, err := s.plan(ctx)
	if err != nil {
		w.Format("ERROR: %v\n", err)
		return
	}

	p.explain(w)
}

func prettyPrint0(protect map[interface{}]struct{}, sf strutil.Formatter, prefix, suffix string, v interface{}) {
	if v == nil {
		return
	}

	switch x := v.(type) {
	case *Token:
		if x == nil {
			return
		}

		sf.Format("%s%v"+suffix, prefix, x.String())
		return
	}

	rt := reflect.TypeOf(v)
	rv := reflect.ValueOf(v)
	switch rt.Kind() {
	case reflect.Slice:
		if rv.Len() == 0 {
			return
		}

		sf.Format("%s[]%T{ // len %d%i\n", prefix, rv.Index(0).Interface(), rv.Len())
		for i := 0; i < rv.Len(); i++ {
			prettyPrint0(protect, sf, fmt.Sprintf("%d: ", i), ",\n", rv.Index(i).Interface())
		}
		sf.Format("%u}" + suffix)
	case reflect.Struct:
		sf.Format("%s%T{%i\n", prefix, v)
		for i := 0; i < rt.NumField(); i++ {
			f := rv.Field(i)
			if !f.CanInterface() {
				continue
			}

			prettyPrint0(protect, sf, fmt.Sprintf("%s: ", rt.Field(i).Name), ",\n", f.Interface())
		}
		sf.Format("%u}" + suffix)
	case reflect.Ptr:
		if rv.IsNil() {
			return
		}

		rvi := rv.Interface()
		if _, ok := protect[rvi]; ok {
			sf.Format("%s&%T{ /* recursive/repetitive pointee not shown */ }"+suffix, prefix, rv.Elem().Interface())
			return
		}

		if protect == nil {
			protect = map[interface{}]struct{}{}
		}
		protect[rvi] = struct{}{}
		prettyPrint0(protect, sf, prefix+"&", suffix, rv.Elem().Interface())
	case reflect.Int, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int8:
		if v := rv.Int(); v != 0 {
			sf.Format("%s%v"+suffix, prefix, v)
		}
	case reflect.Uint, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint8:
		if v := rv.Uint(); v != 0 {
			sf.Format("%s%v"+suffix, prefix, rv.Uint())
		}
	case reflect.Bool:
		if v := rv.Bool(); v {
			sf.Format("%s%v"+suffix, prefix, rv.Bool())
		}
	case reflect.String:
		s := rv.Interface().(string)
		if s == "" {
			return
		}

		sf.Format("%s%q"+suffix, prefix, s)
	case reflect.Map:
		keys := rv.MapKeys()
		if len(keys) == 0 {
			return
		}

		var buf bytes.Buffer
		nf := strutil.IndentFormatter(&buf, "· ")
		var skeys []string
		for i, k := range keys {
			prettyPrint0(protect, nf, "", "", k.Interface())
			skeys = append(skeys, fmt.Sprintf("%s%10d", buf.Bytes(), i))
		}
		sort.Strings(skeys)
		sf.Format("%s%T{%i\n", prefix, v)
		for _, k := range skeys {
			si := strings.TrimSpace(k[len(k)-10:])
			k = k[:len(k)-10]
			n, _ := strconv.ParseUint(si, 10, 64)
			mv := rv.MapIndex(keys[n])
			prettyPrint0(protect, sf, fmt.Sprintf("%s: ", k), ",\n", mv.Interface())
		}
		sf.Format("%u}" + suffix)
	default:
		panic(fmt.Sprintf("prettyPrint: missing support for reflect.Kind == %v", rt.Kind()))
	}
//.........这里部分代码省略.........