Raw Expression select with value
Yeah, only works like this in where clauses right now.  Will look into it
 I'm actually not sure whether this is a valid use-case -- in your example you are querying for the first letter of a constant ("myFirstName") -- what is the benefit of doing that?

I'm assuming the query you're hoping to generate is something like (using sqlite style parameter interpolation):

``` python
>>> query = User.select(['id', 'username', R('LOWER(SUBSTR( %s, 1, 1))', 'myFirstName' , 'first_letter')])
>>> query.sql()
('SELECT "id", LOWER(SUBSTR(?, 1, 1)) AS first_letter FROM "users"', ['myFirstName'])
```

But if you know the "first_letter" is always going to be 'm' why add it to the query?  If you hope to use that alias as part of the where clause you could instead write:

``` python
>>> query = User.select().where(R('LOWER(SUBSTR(username, 1, 1))=%s', 'm'))
>>> query.sql()
('SELECT "id", "username" FROM "users" WHERE LOWER(SUBSTR(username, 1, 1))=?', ['m'])
```

Am I missing something?  I've got this written in a branch but as I was thinking about it I had a hard time thinking of how it would be useful.  Thanks!

Hello Charles, 

want to use 'select' in the following way. 

  << User.select(['id', 'username', R('LOWER(SUBSTR( %s, 1, 1))', 'myFirstName' , 'first_letter')]) >>

but there is no implementation using values and alias together ? 
Have you any idea how to fix it? 

Kind regards, 

Chris
