Update querying_basics.md

[wawashra]

Edit the last example to use subquery rather than ^, because it has an error

iex(76)> movies = from m in Movie, where: [title: "good will hunting"]
#Ecto.Query<from m0 in Friends.Movie, where: m0.title == "good will hunting">
iex(77)>
nil
iex(78)> characters_query = from c in Character,
...(78)> join: ^movies,
...(78)> on: [id: c.movie_id], # keyword list
...(78)> where: c.name == "Wade Watts",
...(78)> select: {m.title, c.name}
** (Ecto.Query.CompileError) unbound variable m in query. If you are attempting to interpolate a value, use ^var
(ecto 3.11.1) expanding macro: Ecto.Query.select/3
iex:78: (file)
(ecto 3.11.1) expanding macro: Ecto.Query.from/2
iex:78: (file)

To verify I used the same format to make a query on my local DB, using the movie title, and verifying the characters of the movie,

The results are

`iex(71)> movies = from m in Movie, where: [title: "good will hunting"]
#Ecto.Query<from m0 in Friends.Movie, where: m0.title == "good will hunting">
iex(72)>
nil
iex(73)> characters_query = from c in Character,
...(73)> join: m in subquery(movies),
...(73)> on: [id: c.movie_id], # keyword list
...(73)> select: {m.title, c.name}
#Ecto.Query<from c0 in Friends.Character,
join: m1 in subquery(from m0 in Friends.Movie,
where: m0.title == "good will hunting"),
on: m1.id == c0.movie_id, select: {m1.title, c0.name}>
iex(74)>
nil
iex(75)> Repo.all(characters_query)

10:45:53.327 [debug] QUERY OK source="characters" db=15.8ms idle=1525.6ms
SELECT s1.title, c0.name FROM characters AS c0 INNER JOIN (SELECT sm0.id AS id, sm0.title AS title, sm0.tagline AS tagline, sm0.inserted_at AS inserted_at, sm0.updated_at AS updated_at FROM movies AS sm0 WHERE (sm0.title = 'good will hunting')) AS s1 ON s1.id = c0.movie_id []
[
{"good will hunting", "Will Hunting"},
{"good will hunting", "Sean Maguire"},
{"good will hunting", "Skylar"}
]`