timestamp auto update
Sure, with the caveat that the new value will not be available to your code unless you explicitly re-fetch the new value.

```python
class TimestampTest(Model):
    name = CharField(max_length=20)
    create_time = DateTimeField(constraints=[SQL('DEFAULT CURRENT_TIMESTAMP')])
    last_modify_time = DateTimeField(constraints=[SQL('DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP')])
``` Thanks, but I find it can only be useful when using Model.update(). If I use Model.save(), it doesn't auto update.

```
    query = TimestampTest.update(name="37a_000").where(TimestampTest.id == 1)
    query.execute()
```
This will update the last_modify_time.

```
    test = TimestampTest.get(id=1)
    test.name = "37a_0a"
    test.save()
```
This doesn't update. Good point. You'll need to specify that peewee should only save the name field:

```python
test.save(only=(TimestampTest.name,))
```

That ought to do the trick.
Can peewee support auto update time when modify data? Like in MySql, it can use "ON UPDATE CURRENT_TIMESTAMP":
```
CREATE TABLE `timestampTest` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`last_modify_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP)
```