Execute a simple SQL report using Rust and Diesel

main.rs

#[macro_use]
extern crate diesel;

use diesel::prelude::*;

table! {
    users (id) {
        id -> Int4,
        first_name -> Nullable<Varchar>,
        last_name -> Nullable<Varchar>,
    }
}

#[derive(Queryable)]
pub struct User {
    pub id: i32,
    pub first_name: Option<String>,
    pub last_name: Option<String>,
}

fn main() {
    let database_url = "postgres://pat@localhost:5432/names";
    let connection = PgConnection::establish(&database_url).expect(
        &format!("Error connecting to {}", database_url)
    );
    println!("Connected!");

    use users::dsl::*;

    let results = users.load::<User>(&connection).expect(
        "Error loading users"
    );

    let (mult, one): (Vec<User>, Vec<User>) =
        results.into_iter().partition(|user|
            if let Some(ref name) = user.last_name {
                name.split(' ').count() > 1
            } else {
                false
            }
        );

    println!("Found {} users with more than one last name.", mult.len());
    println!("Found {} users with one last name.", one.len());
}