If I have to find all uses that viewed the same video more than once, then I'm using the following query.
SELECT userid AS users,video_id
FROM watching_list GROUP BY userid , video_id HAVING COUNT(*) > 1;
^^It does give you that, right? If watching_list contains userid and videoid that the user watched and datetime stamp.
What I would like to do is join it to user table, based on userid, to look up user's name etc too and not just the userid.
I tried doing simple join, and of course it broke over me.
SELECT Users.Name, Users.userid AS users,video_id
FROM watching_list
JOIN Users
ON Users.UserID = watching_list.UserID
GROUP BY Users.userid , video_id, Users.Name
HAVING COUNT(*) > 1;
Why would this break? It should be the same user, so adding additional info of the same person to the group by should not cause a change
Here is a crude, quick SQLFiddle to prove this
A somewhat inelegant way to do it is like so:
Select USERS.LAST_NAME,
USERS.FIRST_NAME,
double_watchers.VIDEO_ID
FROM USERS,
(SELECT userid AS users,
video_id
FROM watching_list
GROUP BY userid , video_id
HAVING COUNT(*) > 1) double_watchers
Where double_watchers.userid = users.id;
I'm creating an inline table (not sure about terminology) with your original query and then joining it to the USERS table. There's probably a much more efficient way to do it, but I don't have a test instance in front of me to experiment right now.
Related
Suppose I have two tables,
User
Post
Posts are made by Users (i.e. the Post Table will have foreign key of user)
Now my question is,
Print the details of all the users who have more than 10 posts
To solve this, I can type the following query and it would give me the desired result,
SELECT * from USER where user_id in (SELECT user_id from POST group by user_id having count(user_id) > 10)
The problem occurs when I also want to print the Count of the Posts along with the user details. Now obtaining the count of user is not possible from USER table. That can only be done from POST table. But, I can't get two values from my subquery, i.e. I can't do the following,
SELECT * from USER where user_id in (SELECT user_id, **count(user_id)** from POST group by user_id having count(user_id) > 10)
So, how do I resolve this issue? One solution I know is this, but this I think it would be a very naive way to resolve this and will make the query much more complex and also much more slow,
SELECT u.*, (SELECT po.count(user_id) from POST as po group by user_id having po.count(user_id) > 10) from USER u where u.user_id in (SELECT p.user_id from POST p group by user_id having p.count(user_id) > 10)
Is there any other way to solve this using subqueries?
Move the aggregation to the from clause:
SELECT u.*, p.num_posts
FROM user u JOIN
(SELECT p.user_id, COUNT(*) as num_posts
FROM post p
GROUP BY p.user_id
HAVING COUNT(*) > 10
) p
ON u.user_id = p.user_id;
You can do this with subqueries:
select u.*
from (select u.*,
(select count(*) from post p where p.user_id = u.user_id) as num_posts
from users u
) u
where num_posts > 10;
With an index on post(user_id), this might actually have better performance than the version using JOIN/GROUP BY.
You can try by joining the tables, Prefer to do a JOIN than using SUBQUERY
SELECT user.*, count( post.user_id ) as postcount
FROM user LEFT JOIN post ON users.user_id = post.user_id
GROUP BY post.user_id
HAVING postcount > 10 ;
That's my database design.
I need to find the person with the most albums using SQLite.
I tried this:
SELECT USERS.NAME, COUNT(USERS.NAME) AS 'value_occurrence' FROM USERS
INNER JOIN ALBUMS
ON USERS.ID = ALBUMS.USER_ID
GROUP BY USERS.NAME
ORDER BY 'value_occurrence'
DESC LIMIT 1;
but it didn't work and gave me the wrong result. Please help me find the right way to do this.
The logic is correct, but you may be getting tripped up by incorrect use of single quotes for aliases. Try this version:
SELECT u.NAME, COUNT(u.NAME) AS value_occurrence
FROM USERS u
INNER JOIN ALBUMS a ON a.USER_ID = u.ID
GROUP BY u.NAME
ORDER BY value_occurrence DESC
LIMIT 1;
The problem with ORDER BY 'value_occurrence' is that you are telling SQLite to order by a constant value. That is, every record in the result set will have the same value for ordering, which basically means that SQLite is free to choose any record as being the "first."
Note: As the answer by #Cazzym mentioned, you should be aggregating by the user ID, in case two or more users might have the same name.
The code basically looks fine, but it will return unexpected results where two users have the same name. That's why we have ID columns!
Try
SELECT USERS.NAME, COUNT(USERS.ID) AS 'value_occurrence' FROM USERS
INNER JOIN ALBUMS
ON USERS.ID = ALBUMS.USER_ID
GROUP BY USERS.ID, USERS.NAME
ORDER BY 'value_occurrence'
DESC LIMIT 1;
We can use group by Users.Id, Users.Name because each ID is going to only have one name associated with it, so it's still going to only create a single group per ID.
I am trying to formulate a single SQL query that will count a table across a one to many relationship. Here is the short version of my schema:
User(id)
Group(id)
UserGroup(user_id, group_id)
Post(id, user_id, group_id)
The goal is to return the count of posts for each user in a group. The specific issue I am running into is my current query cannot return 0 for a user that has no posts. Here is my naive query:
SELECT
COUNT(*) as total,
user_id
FROM
posts
WHERE
group_id = ?
GROUP BY user_id
ORDER BY
total DESC
This works fine when every user has a post, but when some have no posts, they do not show up in the list. How can I write a single query that handles this scenario and returns count 0 for said users? I know I need to somehow incorporate UserGroup to get the list of users, but am stuck from there.
Use a left join:
SELECT u.id, COUNT(*) as total
FROM users u LEFT JOIN
posts p
ON p.user_id = u.id AND
p.group_id = ?
GROUP BY u.id
ORDER BY total DESC
I think I got it, but not sure how performant.
select count(p), u.id from users u left join (select * from workouts where group_id = ?) p on p.user_id = u.id where u.id in (select user_id from user_group where group_id = ?) group by u.id;
I have a users table and a songs table, I want to select all the users in the users table while counting how many songs they have in the songs table. I have this SQL but it doesn't work, can someone spot what i'm doing wrong?
SELECT jos_mfs_users.*, COUNT(jos_mfs_songs.id) as song_count
FROM jos_mfs_users
INNER JOIN jos_mfs_songs
ON jos_mfs_songs.artist=jos_mfs_users.id
Help is much appreciated. Thanks!
The inner join won't work, because it joins every matching row in the songs table with the users table.
SELECT jos_mfs_users.*,
(SELECT COUNT(jos_mfs_songs.id)
FROM jos_mfs_songs
WHERE jos_mfs_songs.artist=jos_mfs_users.id) as song_count
FROM jos_mfs_users
WHERE (SELECT COUNT(jos_mfs_songs.id)
FROM jos_mfs_songs
WHERE jos_mfs_songs.artist=jos_mfs_users.id) > 10
There's a GROUP BY clause missing, e.g.
SELECT jos_mfs_users.id, COUNT(jos_mfs_songs.id) as song_count
FROM jos_mfs_users
INNER JOIN jos_mfs_songs
ON jos_mfs_songs.artist=jos_mfs_users.id
GROUP BY jos_mfs_users.id
If you want to add more columns from jos_mfs_users in the select list you should add them in the GROUP BYclause as well.
Changes:
Don't do SELECT *...specify your fields. I included ID and NAME, you can add more as needed but put them in the GROUP BY as well
Changed to a LEFT JOIN - INNER JOIN won't list any users that have no songs
Added the GROUP BY so it gives a valid count and is valid syntax
SELECT u.id, u.name COUNT(s.id) as song_count
FROM jos_mfs_users AS u
LEFT JOIN jos_mfs_songs AS S
ON s.artist = u.id
GROUP BY U.id, u.name
Try
SELECT
*,
(SELECT COUNT(*) FROM jos_mfs_songs as songs WHERE songs.artist=users.id) as song_count
FROM
jos_mfs_users as users
This seems like a many to many relationship. By that I mean it looks like there can be several records in the users table for each user, one of each song they have.
I would have three tables.
Users, which has one record for each user
Songs, which has one record for each song
USER_SONGS, which has one record for each user/song combination
Now, you can do a count of the songs each user has by doing a query on the intermediate table. You can also find out how many users have a particular song.
This will tell you how many songs each user has
select id, count(*) from USER_SONGS
GROUP BY id;
This will tell you how many users each song has
select artist, count(*) from USER_SONGS
GROUP BY artist;
I'm sure you will need to tweak this for your needs, but it may give you the type of results you are looking for.
You can also join either of these queries to the other two tables to find the user name, and/or artist name.
HTH
Harv Sather
ps I am not sure if you are looking for song counts or artist counts.
You need a GROUP BY clause to use aggregate functions (like COUNT(), for example)
So, assuming that jos_mfs_users.id is a primary key, something like this will work:
SELECT jos_mfs_users.*, COUNT( jos_mfs_users.id ) as song_count
FROM jos_mfs_users
INNER JOIN jos_mfs_songs
ON jos_mfs_songs.artist = jos_mfs_users.id
GROUP BY jos_mfs_users.id
Notice that
since you are grouping by user id, you will get one result per distinct user id in the results
the thing you need to COUNT() is the number of rows that are being grouped (in this case the number of results per user)
Have a table users and there is a field invited_by_id showing user id of the person who invited this user. Need to make a MySQL query returning rows with all the fields from users plus a invites_count field showing how many people were invited by each user.
Something like this:
SELECT
User.*, Count.count
FROM
users AS User,
(
SELECT COUNT(*) AS count FROM users WHERE users.invited_by_id=User.id
) AS Count;
This one is not working so I need a working one.
SELECT u.*,
(
SELECT COUNT(*)
FROM users ui
WHERE ui.invited_by_id = u.id
) AS cnt
FROM users u
Ok, first of all, count is a reserved word in sql so you can't use it as a table alias (unless you quote it in some way but don't do that). Secondly, the real way to solve this problem is to introduce a GROUP BY clause in your subquery.
Try this:
SELECT user3.*, subquery.theCount FROM
users AS user3
INNER JOIN (
SELECT
user1.id, count(user2.id) AS theCount
FROM
users AS user1
LEFT OUTER JOIN
users AS user2 ON user2.invited_by_id=user1.id
GROUP BY user1.id
) AS subquery ON subquery.id=user3.id;
Here is a dirty little secret about MySQL: It lets you cheat with the GROUP BY statement and select columns that are not in the GROUP BY list and also not in aggregate functions. Other RMDMSes don't let you do this.
SELECT
user1.*, count(user2.id) AS theCount
FROM
users AS user1
LEFT OUTER JOIN
users AS user2 ON user2.invited_by_id=user1.id
GROUP BY user1.id;