SQLite3，将多行合二为一

Question

I have two tables cities (as C) and routes (as R)

C:

 ____ ______
| id | city |
|____|______|
| 1  |  A   |
| 2  |  B   |
|____|______|

R:

 ____ ______ ____ __________
| id | from | to | distance |
|____|______|____|__________|
| 1  |  1   | 2  | 100      |
| 2  |  2   | 1  | 100      |
|____|______|____|__________|

(my expectation): I want to combine and join my tables to the following form:

 ____ ______ ____________ ____ __________ __________
| id | from | fromAsText | to | toAsText | distance |
|____|______|____________|____|__________|__________|
| 1  | 1    | A          | 2  | B        | 100      |
| 2  | 2    | B          | 1  | A        | 100      | 
|____|______|____________|____|__________|__________|

To add one value isn't a problem

    SELECT
    r.*
    s.city as fromAsText
    FROM
    routes as r,
    cities as s
    WHERE
    r.from = s.id

But I haven't any Ideas how to achieve my goals! Thanks!

Answer 1

Simply join the city table twice:

select r.id, r.from, c_from.city as from_city, r.to, c_to.city as to_city, r.distance
from routes r
join cities c_from on c_from.id = r.from
join cities c_to on c_to.id = r.to
order by r.id;