I have these tables:
Movies (id, name)
Cast (idmovie, actor)
And I would like to count the number of actors for each movie and then only get movies with more than 10 actors. I have a query to count the number of actors for each movie, which goes like this:
SELECT idmovie, count(actor) FROM Cast GROUP BY idmovie HAVING count(actor) > 10;
Now, I wonder how to get that result and join it to the Movies table.
I tried:
SELECT name FROM Movies INNER JOIN (SELECT idmovie FROM Cast GROUP BY idmovie HAVING count(actor) >2) Cast ON Cast.idmovie = Movies.id;
But it doesn't work.
I also have to translate it to relational algebra.
π name (σ (count(σ id = idmovie))) Movies⨝Cast
Which is obviously wrong...
Any help?
Try this...
SELECT m.name, COUNT(c.actor) AS 'ActorsCount'
FROM Movies m INNER JOIN [Cast] c ON m.id = c.idmovie
GROUP BY m.name HAVING COUNT(c.actor) > 10;
The query looks correct to me except perhaps that you aliased the nested query with Cast which is also the name of a table. I'm not sure what effect that'd have but I'd expect it to confuse MySQL. Try the following:
SELECT name FROM Movies INNER JOIN
(SELECT idmovie FROM Cast GROUP BY idmovie HAVING count(actor) >2) CastCount
ON CastCount.idmovie = Movies.id;
I didn't try it, but I think that'll work
Related
All i want to do is to join two tables, list ALL the rows from the first table, find the average from the second table from all the rows, then list only the ones that are greater than the average.
This is wahat i have done so far, and i am only getting one greater than the average but there are others.
SELECT winner_age, AVG(actor_age) FROM oscar_winners
INNER JOIN actors ON actors.id = oscar_winners.id
WHERE winner_age > (
SELECT AVG(actor_age)
)
You don't really need a join here:
SELECT o.WINNER_AGE
FROM OSCAR_WINNERS o
WHERE o.WINNER_AGE > (SELECT AVG(a.ACTOR_AGE)
FROM ACTORS a)
Something like this?
SELECT actors.*, (SELECT AVG(actor_age) from actors) as average
FROM oscar_winners
INNER JOIN actors ON actors.id = oscar_winners.id and actors.winner_age > (SELECT AVG(actor_age) from actors)
The problem with your query is because you are using a where clause, while you should probably be using having:
SELECT w.winner_age, AVG(a.actor_age)
FROM oscar_winners w
INNER JOIN actors a
ON actors.id = oscar_winners.id
group by w.winner_age
having w.winner_age > AVG(a.actor_age)
I'm just playing around with SQL and I'm trying to do the following.
I have 2 tables and here is their structure:
Movies_metadata Movies
ratings table:
Ratings
As there are many ratings for one movie, what I'd like to do is get the avg rating per movie and have it display next to the title which is only available in the Metadata table.
This is as far as I got but obviously the issue with my SELECT statement is that it'll return the average of all movies and display it for each record:
SELECT
(SELECT
AVG(rating)
FROM
`movies-dataset.movies_data.ratings`) AS rating_avg,
metadata.title,
metadata.budget,
metadata.revenue,
metadata.genres,
metadata.original_language,
metadata.release_date
FROM
`movies-dataset.movies_data.Movies_metadata` AS metadata
INNER JOIN `movies-dataset.movies_data.ratings` AS ratings
ON metadata.id = ratings.movieId
LIMIT 10
Here is an example of the result:
Result
I'm thinking I can potentially use a GROUP BY but when I try, I get an error
Appreciate the help!
The following should work:
SELECT movies_metadata.title, AVG(ratings.rating)
FROM movies_metadata
LEFT JOIN ratings ON movies_metadata.id = ratings.movieID
GROUP BY movies_metadata.title
You can swap movies_metadata.title by movies_metadata.id if not unique.
The LIMIT function and GROUP function might conflict with each other. Try getting the average rating as part of the inner join like this:
SELECT
ratings.averagerating,
metadata.title,
metadata.budget,
metadata.revenue,
metadata.genres,
metadata.original_language,
metadata.release_date
FROM `movies-dataset.movies_data.Movies_metadata` AS metadata
INNER JOIN (SELECT movieId, AVG(rating) averagerating FROM `movies-dataset.movies_data.ratings` GROUP by movieId) AS ratings
ON metadata.id = ratings.movieId
ORDER BY ratings.averagerating
LIMIT 5
Maybe try something like:
Select m.movieID, (r.rate_sum / r.num_rate) as avg_rating
From your_movies_table m
Left Join (select movie_id, sum(rating) as ‘rate_sum’, count(rating) as ‘num_rate’
From your_ratings_table
Group by movie_id) r
On m.movie_id = r.movie_id
I'm using a left join because I'm not sure if all movies have been rated at least once.
I would very much appreciate your help with this query. My database (Oracle) has a table called MOVIES with fields like id and title. Then there is another one, SCORES which has fields like movie_id and score. It is a one-to-many relation.
Now, I'm looking for a way to get a SELECT that will give me a result like one below:
movie-title, avg(score where movie.id=scores.movie_id)
It looks simple at first glance, but I cannot pass through it. Any suggestions?
First off, you need to join the tables on the pk/fk
Then, in order to get the avg for each movie, you need to use group and specify the column (score) that you want.
In this case we are grouping by the id because it's unique and the movie title since it is in the select clause
select m.title, avg(s.score)
from movie m
inner join scores s
on m.id = s.movie_id
group by m.id, m.title
You just need join and group by as follows:
Select m.title, avg(s.score)
From movies m join scores s
On m.id = s.movie_id
Group by m.id, m.title
Sorry I'm new here and I'm also new with SQL and can't really explain my problem in the title...
So I have a TV show database, and there I have a Genre column, but for a TV show there are multiple Genres stored, so when I'm selecting all my TV Shows how can I combine them?
It needs to look like this:
https://i.stack.imgur.com/3EhBj.png
So I have to combine the string together, here is my code so far what I wrote:
SELECT title,
year,
runtime,
MIN(name) as name,
ROUND(rating, 1) as rating,
trailer,
homepage
FROM shows
JOIN show_genres
on shows.id = show_genres.show_id
JOIN genres
on show_genres.genre_id = genres.id
GROUP BY title,
year,
runtime,
rating,
trailer,
homepage
ORDER BY rating DESC
LIMIT 15;
I also have some other stuff here, that's my exerciese tasks! Thanks!
Also here is the relationship model:
https://i.stack.imgur.com/M89ho.png
Basically you need string aggregation - in Postgres, you can use string_agg() for this.
For efficiency, I would recommend moving the aggregation to a correlated subquery or a lateral join rather than aggregating in the outer query, so:
SELECT
s.title,
s.year,
s.runtime,
g.genre_names,
ROUND(s.rating, 1) as rating,
s.trailer,
s.homepage
FROM shows s
LEFT JOIN LATERAL (
SELECT string_agg(g.name, ', ') genre_names
FROM show_genres sg
INNER JOIN genres g ON g.id = sg.genre_id
WHERE sg.show_id = s.id
) g ON 1 = 1
ORDER BY s.rating DESC
LIMIT 15
I'm writing a query to multiply the count that I receive from subquery to fees amount, But I don't know how to do that. Any help/suggestion?
Oracle query is:
select courseid,coursename,fees*tmp
from course c join registration r on
r.courseid=c.courseid
and tmp IN (select count(*)
from course c join registration r on
r.courseid=c.courseid group by coursename);
I tried to use like a variable tmp ,But i don't think it works in oracle query. Is there an alternative way to do so?
You can't do that, because you can only select data from tables that appeared between FROM and WHERE. The IN operator is a quick way to save having to write a bunch of OR statements, it is not something that can establish a variable in the outer query.
Instead do something like:
select courseid,coursename,fees * COUNT(r.courseID) OVER(PARTITION BY c.coursename)
from course c join registration r on
r.courseid=c.courseid
Edit/update: you noted that this query produces too many rows and you only want to see distinct course names. In that case it would be better to just use the registrations table to count the number of people on the course and then multiply the fees:
SELECT
c.courseid, c.coursename, c.fees * COALESCE(r.numberOfstudents, 0) as courseWorth
FROM
course c
LEFT OUTER JOIN
(select courseid, COUNT(*) as numberofstudents FROM registration GROUP BY courseid) r
ON c.courseID = r.courseid
You can use a windowing function like Caius or you can use a join like this:
select courseid,coursename, fees * COALESCE(sub.cnt,0)
from course c
join registration r on r.courseid=c.courseid
left join (
select coursename, count(*) as cnt
from course c2
join registration r2 on r2.courseid=c2.courseid
group by coursename
) as sub;
note: I make no claim your joins are correct -- I'm basing this query off of your example not on any knowledge of your data model.