diff --git a/dbmap.go b/dbmap.go
index 01b218d..8a761d3 100644
--- a/dbmap.go
+++ b/dbmap.go
@@ -4,29 +4,42 @@ import (
 	"reflect"
 )
 
+const tagName = "db"
+
 func Columns(t reflect.Type) []string {
-	vs := make([]string, t.NumField())
+	var vs []string
 	for i := 0; i < t.NumField(); i++ {
-		vs[i] = t.Field(i).Tag.Get("db")
+		tag := t.Field(i).Tag.Get(tagName)
+		if tag == "" {
+			continue
+		}
+		vs = append(vs, tag)
 	}
 	return vs
 }
 
 func Values(s any) []any {
 	v := reflect.ValueOf(s)
-	vs := make([]interface{}, v.NumField())
+	t := reflect.TypeOf(s)
+	var vs []any
 	for i := 0; i < v.NumField(); i++ {
-		vs[i] = v.Field(i).Interface()
+		if t.Field(i).Tag.Get(tagName) == "" {
+			continue
+		}
+		vs = append(vs, v.Field(i).Interface())
 	}
 	return vs
 }
 
 func Scan(s any) []any {
-	vo := reflect.ValueOf(s).Elem()
-	vs := make([]interface{}, vo.NumField())
-	for i := 0; i < vo.NumField(); i++ {
-		f := vo.Field(i)
-		vs[i] = f.Addr().Interface()
+	v := reflect.ValueOf(s).Elem()
+	t := reflect.TypeOf(s).Elem()
+	var vs []any
+	for i := 0; i < v.NumField(); i++ {
+		if t.Field(i).Tag.Get(tagName) == "" {
+			continue
+		}
+		vs = append(vs, v.Field(i).Addr().Interface())
 	}
 	return vs
 }
diff --git a/dbmap_test.go b/dbmap_test.go
index 5ac5bd9..db7d3d8 100644
--- a/dbmap_test.go
+++ b/dbmap_test.go
@@ -7,9 +7,11 @@ import (
 )
 
 type Entity struct {
-	Id        int       `db:"id"`
-	Name      string    `db:"name"`
-	CreatedAt time.Time `db:"created_at"`
+	Id            int       `db:"id"`
+	NullableField *int      `db:"nullable_field"`
+	Name          string    `db:"name"`
+	CreatedAt     time.Time `db:"created_at"`
+	FieldNotIdDb  int
 }
 
 func TestColumns(t *testing.T) {
@@ -28,6 +30,7 @@ func TestColumns(t *testing.T) {
 			},
 			want: []string{
 				"id",
+				"nullable_field",
 				"name",
 				"created_at",
 			},
@@ -47,9 +50,10 @@ func TestScan(t *testing.T) {
 		s any
 	}
 	e := Entity{
-		Id:        1,
-		Name:      "Test",
-		CreatedAt: time.Now(),
+		Id:            1,
+		NullableField: nil,
+		Name:          "Test",
+		CreatedAt:     time.Now(),
 	}
 	tests := []struct {
 		name string
@@ -63,6 +67,7 @@ func TestScan(t *testing.T) {
 			},
 			want: []any{
 				&e.Id,
+				&e.NullableField,
 				&e.Name,
 				&e.CreatedAt,
 			},
@@ -98,6 +103,7 @@ func TestValues(t *testing.T) {
 			},
 			want: []any{
 				e.Id,
+				e.NullableField,
 				e.Name,
 				e.CreatedAt,
 			},