So i am making this webpage (for fun to practice web dev) where users can rate or comment on a movie. One page I have is where you click on the movie for full details and it lists all the ratings and comments (together if the user has commented by review and rated through a page called "reviewMovie"...which if they went this way the rating is mandatory, otherwise they can comment on this page "listMovieReviews").
The problem I am having is incorrect details when doing my queries
the discussion table stores: the discussion ID (primary key) the timestamp of the
comment, the comment, the user who made the comment, and the movie they commented
about.
the discussion table stores: the discussion ID (primary key) the timestamp of the
comment, the comment, the user who made the comment, and the movie they commented
about.
the rating table stores: the rating ID (primary key), the movie being rated, the
user who did the rating, and the rating score (out of 10)
So some examples of the combined data are:
User1 (user1) has rated "American Psycho" a 4/10 and has made a comment "comment1" on
it
User2 (admin..for testing purposes) has rated "American Psycho" a 8/10 and has made a
comment "comment2" on it
So on the page that lists the details of "American Psycho" and the ratings/comments I should have this list of ratings and comments:
<TIMESTAMP FOR COMMENT1> User1 Rating 4/10 "comment1"
<TIMESTAMP FOR COMMENT2> admin Rating 8/10 "comment2"
Using the following queries:
SELECT *
FROM discussion
INNER JOIN users ON discussion.userID = users.userID
WHERE discussion.movieID = <American Psycho's Movie ID>;
AND
SELECT *
FROM ratings
INNER JOIN movies ON ratings.movieID = movies.movieID
WHERE ratings.movieID = <American Psycho's Movie ID>;
I get this:
<TIMESTAMP FOR COMMENT2> admin Rating 4/10 "comment2"
<TIMESTAMP FOR COMMENT2> admin Rating 8/10 "comment2"
I have tried several other INNER JOINS with joining the table that stores user information and table that stores movies information but I keep getting mixed data
Also tried DISTINCT and UNION but still to no avail
Where am I going wrong??
Also first post so sorry If I have not been too clear, bad formatting, or not shown enough work but I am really really stuck
I assume:
A movie could have from 0 to n comments.
A movie could have from 0 to n ratings.
A user could rate a movie only once or none.
A user could comment a movie from 0 to n times.
Your queries are fine, maybe your problem is in your php code.
You have to account that a user maybe comment a movie several time and never rated it.
In second query you should JOIN with user (instead of with movie, because you do not get movie information) to get the user name.
Maybe you should display the info in two table: one for ratings and other for comments.
(You have to replace quotation marks by movie ID)
SELECT u.userName, r.score
FROM ratings AS r
INNER JOIN users AS u ON r.userID = u.userID
WHERE r.movieID = ?;
SELECT u.userName, d.commentTime, d.comment
FROM discussion AS d
INNER JOIN users AS u ON d.userID = u.userID
WHERE d.movieID = ?;
You could group all comments per user in one row this way (but I think this is not what you are looking for):
SELECT u.userName, GROUP_CONCAT(CONCAT(d.commentTime, ': ', d.comment) SEPARATOR '; ') AS comments
FROM discussion AS d
INNER JOIN users AS u ON d.userID = u.userID
WHERE d.movieID = ?
GROUP BY u.userName
I think do not have sense to make one query in this case, but if you want get all data in one query you could try something like this:
You will have a comment per row, so for example if a user make two comment you will have two rows for the same user with the same score.
First I get all user that comment or rating the selected movie and make a CROSS JOIN between movie and these users. Then I make a LEFT JOIN with discussion ON movieID and userID and another LEFT JOIN with ratings ON movieID and userID.
You need to make LEFT JOIN instead of INNER JOIN because if a movie do not have ratings or comments your result will be empty.
In SELECT clause you should list only the columns that you need.
SELECT *
FROM movies m
CROSS JOIN (SELECT d.userID
FROM discussion d
WHERE d.movieID = ?
UNION
SELECT r.userID
FROM ratings r
WHERE r.movieID = ?) AS u
LEFT JOIN discussion AS d ON m.movieID = d.movieID AND u.userID = d.userID
LEFT JOIN ratings AS r ON m.movieID = r.movieID AND u.userID = r.userID
LEFT JOIN users ON u.userID = users.userID
WHERE m.movieID = ?;
You need to join all three tables.
SELECT *
FROM movies AS m
JOIN ratings AS r ON r.movieID = m.movieID
JOIN discussion AS d ON d.userID = r.userID AND d.movieID = m.movieID
WHERE m.movieID = <American Psycho's Movie ID>
ORDER BY r.userID, d.timestamp
This will repeat the movie and rating information for each comment. You can remove those duplicates in the application code that displays the results. See How can i list has same id data with while loop in PHP? for an example of how to do this.
SELECT * FROM movies AS MOVIE
JOIN ratings AS RATING ON `RATING.movieID` = `MOVIE.movieID`
JOIN discussion AS DISCUS ON `DISCUS.userID` = `RATING.userID`
WHERE `MOVIE.movieID` = <SOME Movie ID>
ORDER BY `RATING.userID`, `DISCUS.timestamp`
Related
I have 3 tables, users, news, news_viewed. I'm trying to join these 3 tables and find a list of news each user has not viewed.
TABLE users
userid
username
status
TABLE news
newsid
title
post_time
TABLE news_viewed
nvid
username
newsid
Looking to find a list from users that have not read news (found in news_viewed)
I've tried many different joins, including left joins and inners and outers but cannot get the results I need.
$_30daysago = strtotime('-30 days');
SELECT * FROM
(
SELECT users.username, news_id
FROM users inner join news_viewed ON
users.username = news_viewed.username and users.status='active'
UNION
SELECT news_viewed.username, post_time
FROM news_viewed inner join news ON
news_viewed.newsid = news.newsid and news.post_time>'$_30daysago'
) as JoinedTable
I need the required results to include the users.username, news.newsid and news.title.
Any help would be appreciated, thank you!
This is a good spot to use the LEFT JOIN antipattern:
SELECT u.username, n.newsid, n.title
FROM users u
INNER JOIN news n ON n.post_time > ?
LEFT JOIN news_viewed nv
ON n.newsid = nv.newsid
AND nv.username = u.username
WHERE
u.status = 'active'
AND nv.nvid IS NULL
This query generates a cartesian product of users and recent news (ie having a post time greater than the parameter indicated by ?), and returns the users/news tuples for which the left join on news_viewed did not succeed (hence the antipattern).
Note: it is unclear what column to use in the join; column name news_viewed (username) tend to indicate that it relates to users(username), whereas the primary key of users seems to be userid. Fix your column names or fix your relationship.
Ellaborating on #GMB's answer
Your query:
$_30daysago = strtotime('-30 days');
SELECT * FROM
(
SELECT users.username, news_id
FROM users inner join news_viewed ON
users.username = news_viewed.username and users.status='active'
UNION
SELECT news_viewed.username, post_time
FROM news_viewed inner join news ON
news_viewed.newsid = news.newsid and news.post_time>'$_30daysago'
) as JoinedTable
is saying:
get all active users with the news they have read (inner join)
SELECT users.username, news_id
FROM users inner join news_viewed ON
users.username = news_viewed.username and users.status='active'
and add all the news with the users that have read them in the last 30 days (inner join again)
SELECT news_viewed.username, post_time
FROM news_viewed inner join news ON
news_viewed.newsid = news.newsid and news.post_time>'$_30daysago'
That is actually bringing up all the tuples from news_viewed minus the ones where the user is not active AND the new is over 30 days old.
however, given the usage of inner join, you're bringing a lot of duplicate records
1.- The results from the first query where the new is less than 30 days old
2.- The results from the second query where the user is active
since you're using UNION and not UNION ALL, you are implicitly asking for a SELECT DISTINCT, but the fields are different (it makes no sense to display newsid and then post_time in the same field)
plus, you have a typo in the field name, which is not news_id
You have to look at it from the other way around. The potential combinations amount for a scenario where every user has read every new. So you get that universe as a basis (number of users times number of news) and then
1- remove inactive users
2- remove news older than 30 days
3- remove tuples that are unrelated in the news_viewed table
SELECT users.username, news.newsid
FROM users
JOIN news
ON users.status='active' -- removes inactive users
AND news.post_time>'$_30daysago' -- removes older news
LEFT JOIN
news_viewed nv USING (username, newsid)
WHERE nv.nvid IS NULL -- removes unrelated entries
I'm not too good with explaining things, apologies.
I have 3 tables that are similar to the below:
users
id
username
threads
id
title
user_id
lastpost_id
posts
id
content
thread_id
user_id
On a page listing forum threads, I want the username of both the thread author, and the last post author of that thread to be displayed, I'm attempting to achieve this in a single query.
My query looks like this:
SELECT t.*,u.username FROM threads t
INNER JOIN users u ON t.user_id=u.id
INNER JOIN posts p ON t.lastpost_id=p.id
ORDER BY t.id DESC
The first join enables me to get the username of the user id that started the thread.
The second join is what I'm not sure on, it can get me the user id but how do I get the username from that, as a 3rd join?
You can select the same table multiple times if you give it a different alias. You can give the fields aliases too:
SELECT
t.*,
tu.username as threadusername, /* Result field is called 'threadusername' */
p.*,
pu.username as lastpostusername
FROM threads t
INNER JOIN users tu ON t.user_id=tu.id /* thread user */
INNER JOIN posts p ON t.lastpost_id=p.id
INNER JOIN users pu ON p.user_id=pu.id /* post user */
ORDER BY t.id DESC
You can join to a joined table like this:
SELECT t.*,u.username,u2.username FROM threads t
INNER JOIN users u ON t.user_id=u.id
INNER JOIN posts p ON t.lastpost_id=p.id
INNER JOIN users u2 ON p.user_id=u2.id
ORDER BY t.id DESC
Note, I haven't had time to test it, but it should work (at least in MySQL).
I don't know if I got it correctly, but as per my understanding you can have a inner query to fetch the thread ids and then have a outer query to fetch the posts based on the thread id, have a max on post id and group by user id. Also join to user to have the name. Hope that helps.
I have three tables, user, blog and status.
here is sqlFiddle link of my example database
user is the main table where userId and other info of user is store. I want that when I search from table user, the query should also get data from other two tables with specific userId.But only one row from blog which has maximum views,if one blog has same views then which row has max bogId that should come. and sort by views desc, if there is no blog with that userId then sort by should status id.
result comes as i want but, can someone simplify this the query.
sorry for bad English.
Is this anything like what you want ?
SELECT *
FROM user u
LEFT JOIN blog b ON u.userId = b.userId
LEFT JOIN status s ON u.userId = s.userId
WHERE MATCH(u.firstName, u.lastName, u.userName) AGAINST('harry')
GROUP BY u.userId
ORDER BY b.views
I have a table in which I store followers, I have another table in which I store friendships
Now I have third table which stores stream data.
Its a social network, there are many reasons so I don't wish to have one table for follower & friendships (Means facebook subscriptions/friends)
Can someone presents a way how should I query streams table to pick activities of both friends & followings ?
Any help would be really appreciated, thank you
Here is simple Database Scheme, its not really like this but almost!
Okay here is database tables schema please,
Followers table.
Row_ID
User_ID
Following_User_ID
Friends Table
Row_ID
User_ID
Friend_ID
Stream Table
Row_ID
User_ID
Contents_ID
Time
Type
What are you looking for is probably best done as two distinct results sets... or a union of the two.
Select "friend" as src, author, post from friends f inner join streams s on s.author = f.id
union
Select "follower" as src, author, post from followers f inner join streams s on s.author = f.id
This is just some pseudo coding but it should give you an idea of how to proceed. Without knowing your database schema, this is the best I can offer.
Edit:
This might be what your looking for then
select user_id, contents_id, time from (
select user_id, contents_id, time
from followers f inner join stream s on s.user_id = f.user_id and f.user_id = "username"
union
select user_id, contents_id, time
from friends f inner join stream s on s.user_id = f.user_id and f.user_id = "username"
) order by time desc
This will return the data in time order, descending.
I have an application with tutors and courses and subscribers and ratings. These are the tables I am using:
tbl_tutors:
id
name
tbl_subscribers:
id
user_id
course_id
tbl_courses:
id
name
tutor_id
tbl_ratings:
id
user_id
course_id
rating
I need to get 1 tutor with the number of courses he has, the number of total subscribers for those courses and the average course rating for all his courses. This is a lot of data; can it be done in 1 sql query or do I need to code foreach statements in php to get the average ratings and the total subscribers for those courses?
Well do you need totals per tutor-course combination or a total (and average) at the tutor level?
And what is the rating table adding over the subscriber table? Aren't they both unique user-course combinations?
If one user attends multiple courses by the same tutor, how many subscribers do they count as?
The SQL provided by #alfasin is easily extended to all tutors. The syntax below is for SQL server, you may need to change for MySQL
Select t.name, count(distinct c.id) courseCount, count(s.id) subscribers, avg(r.rating) subRating
From tbl_tutors t
Inner join tbl_courses c on c.tutorid = t.id
Inner join tbl_subscribers s on s.courseid = c.id
Inner join tbl_ratings r on r.userid = s.userid and r.courseid = c.id
Group by t.name
Note that when trying to build queries like this it's usually best to do them without grouping so you can inspect which rows are contributing to the counts and ensure you're including everything you expect and that you're not duplicating results
select t.name "Tutor", count(c.id) "# courses", count(s.id) "# subscribers"
from tbl_tutors t, tbl_subscribers s, tbl_courses c, tbl_ratings r
where t.id = XXX
and c.tutor_id = t.id
and s.course_id = c.id
and r.user_id = s.user_id
group by t.name
this sql will get you all you need besides the courses average (substitute the XXX with the tutor-id you want to find). for courses average you can run a separate select.