问题
Ugh ok I'm terrible at explaining things, so I'll just give you the quotes and links first:
Problem 4b (near bottom):
4b. List the film title and the leading actor for all of 'Julie Andrews' films.
movie(id, title, yr, score, votes, director)
actor(id, name)
casting(movieid, actorid, ord)
(Note: movie.id = casting.movieid, actor.id = casting.actorid)
My answer (doesn't work):
SELECT title, name
FROM casting JOIN movie
ON casting.movieid = movie.id
JOIN actor
ON casting.actorid = actor.id
WHERE name = 'Julie Andrews'
AND ord = 1
The problem here is that it wants the list of lead actors of movies with 'Julie Andrews' as an actor (who is not necessarily the lead actor), but all I'm doing with my answer is getting the movies where she is the lead (ord = 1).
How do I specify the list of lead actors without 'Julie Andrews' being it? I suspect I have to do something with GROUP BY, but I can't figure out what at the moment...
Edit: Do I need to use a nested SELECT?
回答1:
There are wonderful ways of doing this with subqueries, but it appears that t this point in the tutorial you're only working with JOINs. The following is how you would do it with only JOINs:
SELECT
movie.title,
a2.name
FROM
actor AS a1
JOIN casting AS c1 ON (a1.id = c1.actorid)
JOIN movie ON (c1.movieid = movie.id)
JOIN casting AS c2 ON (movie.id = c2.movieid)
JOIN actor AS a2 ON (c2.actorid = a2.id)
WHERE
a1.name = 'Julie Andrews'
AND c2.ord = 1
EDIT (more descriptive):
This will give us a table containing all of the movies Julie Andrews acted in. I'm aliasing the actor and casting tables as a1 and c1 respectively because now that we've found a list of movies, we'll have to turn and match that against the casting table again.
SELECT
movie.*
FROM
actor a1
JOIN casting c1 ON (a1.id = c1.actorid)
JOIN movie ON (c1.movieid = movie.id)
WHERE
a1.name = 'Julie Andrews'
Now that we have a list of all movies she acted, we need to join that against the casting table (as c2) and that to the actor table (as a2) to get the list of leading roles for these films:
SELECT
movie.title, -- we'll keep the movie title from our last query
a2.name -- and select the actor's name (from a2, which is defined below)
FROM
actor a1 -- \
JOIN casting AS c1 ON (a1.id = c1.actorid) -- )- no changes here
JOIN movie ON (c1.movieid = movie.id) -- /
JOIN casting AS c2 ON (movie.id = c2.movieid) -- join list of JA movies to the cast
JOIN actor AS a2 ON (c2.actorid = a2.id) -- join cast of JA movies to the actors
WHERE
a1.name = 'Julie Andrews' -- no changes
AND c2.ord = 1 -- only select the star of the JA film
Edit: In aliasing, the 'AS' keyword is optional. I've inserted it above to help the query make more sense
回答2:
You want to match movies to two potentially separate rows in the casting table: one row where Julie Andrews is the actor, and the second row which may or may not be Julie Andrews, but which is the lead actor for the film.
Julie <---> cast in <---> a movie <---> starring <---> Lead actor
So you need to join to the casting table twice.
SELECT m.title, lead.name
FROM actor AS julie
JOIN casting AS c1 ON (julie.id = c1.actorid)
JOIN movie AS m ON (c1.movieid = m.id)
JOIN casting AS c2 ON (m.id = c2.movieid)
JOIN actor AS lead ON (c2.actorid = lead.id)
WHERE julie.name = 'Julie Andrews'
AND c2.ord = 1;
Remember that "table aliases" reference potentially different rows, even if they are aliases to the same table.
回答3:
SELECT title, name
FROM casting JOIN movie
ON casting.movieid = movie.id
JOIN actor
ON casting.actorid = actor.id
WHERE ord = 1
and casting.movieid in
(select movieid
from casting
join actor
on actor.id = casting.actorid
where actor.name = 'Julie Andrews')
回答4:
By the way, this was the answer posted on the site (I just found out about it):
SELECT title, name
FROM movie, casting, actor
WHERE movieid=movie.id
AND actorid=actor.id
AND ord=1
AND movieid IN
(SELECT movieid FROM casting, actor
WHERE actorid=actor.id
AND name='Julie Andrews')
Go figure. :P
回答5:
select title, name from movie join casting on movie.id=movieid
join actor on actor.id=actorid
where ord=1 and movieid in (select movieid from actor join casting
on actor.id=actorid
where name='julie andrews' and (ord=1 or ord<>1))group by title, name
回答6:
@Bill Karwin 's answer is good for the direction. However, the result turns out some movies' title has been appear more than one time. So we need added a DISTINCT function before title in SELECT row.
SELECT DISTINCT m.title, lead.name
And if you want more quick response, you also could write code in this way.
SELECT DISTINCT m.title, lead.name
FROM actor AS julie
JOIN casting AS c1 ON (julie.id = c1.actorid AND julie.name = 'Julie Andrews')
JOIN movie AS m ON (c1.movieid = m.id)
JOIN casting AS c2 ON (m.id = c2.movieid)
JOIN actor AS lead ON (c2.actorid = lead.id)
WHERE c2.ord = 1;
回答7:
I ve done simply like this
select distinct title,name from
(select movie.* from movie
inner join casting on (movie.id = casting.movieid)
inner join actor on (casting.actorid = actor.id)
where actor.name = 'Julie Andrews' ) as moviesFromJulie
inner join casting on (moviesFromJulie.id = casting.movieid)
inner join actor on (casting.actorid = actor.id)
where ord = 1
Retreive all movies julie andrews played in, then for those movies retreive all movies and actors for them with ordinal number = 1, and distinct for unique results
回答8:
Sharing an easy answer to this-
select title, name from movie
join casting on movie.id=movieid
join actor on actor.id=actorid where ord=1 and movie.id in (select movie.id from movie
join casting on movie.id=movieid
join actor on actor.id=actorid where name='Julie Andrews')
回答9:
SELECT title , name
FROM movie JOIN casting ON (casting.movieid=movie.id) JOIN actor ON (actor.id=actorid)
WHERE (movieid IN (SELECT movieid
FROM casting JOIN actor ON (actor.id=actorid)
WHERE name = 'Julie Andrews')) AND (ord=1)
来源：https://stackoverflow.com/questions/434013/how-do-i-list-the-first-value-from-a-three-way-joined-table-query