ORDER BY with multiple DESC fields broken for Postgres
Thank you for pointing this out, I will address this
 You know, I tried to replicate this issue and was not seeing the same problem... can you give any more specifics?

``` python

users = User.select().order_by(User.username.desc(), User.id.desc())
ipdb> users
<class 'tests.User'> SELECT t1."id", t1."username" FROM "users" AS t1 ORDER BY t1."username" DESC, t1."id" DESC []
```

If you have an example that is failing that might help me figure out where the problem is.
 You're right. My example wasn't exactly what I was doing but I assumed it was the same. I am doing

```
users = User.select().order_by([User.username.desc(), User.id.desc()])
```

I am doing it this way b/c in my use case I am assembling a list of order bys.
 I could do 

```
User.select().order_by(*[User.username.desc(), User.id.desc()])
```

to expand the array into the parameter list I guess.
 FYI, I also in my journey tried

```
User.select().order_by(User.username.desc() & User.id.desc())
```

Which results in parens as well. 

This is the wrong way to do it anyway since it is joined with an AND.

```
ORDER BY (t1."username" DESC AND t1."id" DESC)
```
 Yes, the examples you've provided can result in invalid SQL - peewee won't stop you from doing this, however I think the documentation is pretty clear:

http://peewee.readthedocs.org/en/latest/peewee/api.html#SelectQuery.order_by

I'm gonna go ahead and close this as it is working as I intended

If I try to do a 

```
query.order_by(Model.field.desc(), Model.field2.desc())
```

with a Postgres DB the generated SQL will look like

```
ORDER BY (t1.field DESC, t1.field2 DESC)
```

which is invalid SQL for Postgres (not sure on other DBs). Postgres (I think) treats that as the creation of a tuple to sort on, and then complains you can't have DESC in the creation of a tuple.

Removing the parens would fix this issue.
