Inner query problem
Change:

``` python
inner_query = Log.select().order_by(Log.DateTimeUTC.desc()).limit(20)
```

To:

``` python
inner_query = Log.select(Log).order_by(Log.DateTimeUTC.desc()).limit(20)
```

If a subquery does not have an explicit selection, peewee assumes you just want the primary key, hence the missing column.

Hi. I need to execute the following SQL statement but use Peewee's library to do it and prefer not to use raw sql.
Table "Log" has has this structure:

``` sql
CREATE TABLE "Log" ("Id" INTEGER NOT NULL PRIMARY KEY, "DateTimeUTC" DATETIME NOT NULL,  "Value" INTEGER NOT NULL)
```

SQL query needing translation:

``` sql
select * from
    (select * from Log
     order by DateTimeUTC desc
     limit 20
    )
    order by DateTimeUTC
```

I have been helped by the author of Peewee ORM, Charles, with the following code:

``` python
inner_query = Log.select().order_by(Log.DateTimeUTC.desc()).limit(20)
query = Log.select().from_(inner_query).order_by(Log.DateTimeUTC)
```

This generates an error:
`OperationalError: no such column: t1.Id`

I was then given a modification to try:

``` python
inner_query = Log.select().order_by(Log.DateTimeUTC.desc()).limit(20)
inner_query = inner_query.alias('t1')
query = Log.select().from_(inner_query).order_by(Log.DateTimeUTC)
```

However I get another error:
`OperationalError: no such column: t1.DateTimeUTC`

Looking at the debug code Peewee provides:
`[2015-07-22 12:04:23,822] [peewee] DEBUG]: ('SELECT "t1"."Id", "t1"."DateTimeUTC", "t1"."Value" FROM (SELECT "t2"."Id" FROM "Log" AS t2 ORDER BY "t2"."DateTimeUTC" DESC LIMIT 20) AS t1 ORDER BY "t1"."DateTimeUTC" ASC', [])`
It seems that when Peewee is executing the first line of the last snippet `inner_query = Log.select()...`, the conversion to SQL is incorrect and only using the `".Id"` field instead of all fields in the select() and result in the "no such column" error. 

Firstly it seems that the need to add the line `inner_query = inner_query.alias('t1')` looks like a bug as "t1" is not used in my query.

Secondly there seems to be a bug somewhere in translating `select()` to SQL when you have an inner query as only one field is being used when all should be used.

Many thanks
P
