I have the following query:
SELECT users.id, username FROM users
where exists (select 1 from topic_visits tv where users.id = tv.user_id and topic_id = 2)
order by tv.created_at;
I want to retrieve all users who have visited topic 2 in ascending order (oldest visit first).
I got this error: #1054 - Unknown column 'tv.created_at' in 'order clause'.
You can change your query as shown below:
SELECT distinct users.id, username,tv.created_at
FROM users
join topic_visits tv ON users.id = tv.user_id and topic_id = 2
order by tv.created_at
tv is in the sub-query, it doesn't exist at the top level.
using a join, we group by users.id so there is a unique list of users.
As the tv.created_at could be multiple we need to wrap it in an aggregate function, in this case MAX. Maybe MIN suites your needs better however.
SELECT users.id, username
FROM users
join topic_visits tv ON users.id = tv.user_id and topic_id = 2
group by users.id
order by MAX(tv.created_at);
Related
There are three tables, I would like to get the count of a user's total tweets and the count of likes his total tweets received.
I tried to combine two queries to get what I want but failed. Have looked through several previous questions but still can't figure it out.
Users table
id
name
1
User1
Tweets table
id
UserId (foreign key)
content
1
User1
hello
Likes table
id
UserId (foreign key)
TweetId (foreign key)
1
User1
hello
First query:
SELECT Users.name, Users.id, COUNT(Tweets.UserId) AS UserTweetCount FROM Users
LEFT JOIN Tweets
ON Users.id = Tweets.UserId
GROUP BY Users.id
ORDER BY UserTweetCount DESC;
Second query:
SELECT Users.name, Users.id, COUNT(Likes.UserId) AS UserTweetBeLikedCount FROM Users
LEFT JOIN Likes
ON Users.id = Likes.UserId
GROUP BY Users.id;
I tried like below but would get wrong UserTweetBeLikedCount counts. The counts would be UserTweetCount's, not UserTweetBeLikedCount's. When I ran two queries separately, it worked well. But when I combined them together, it didn't work right.
Don't know how to display the right counts. Can someone give me hints to solve this, please?
SELECT Users.name, Users.id,
COUNT(Tweets.UserId) AS UserTweetCount, COUNT(Likes.UserId) AS UserTweetBeLikedCount
FROM Users
LEFT JOIN Tweets
ON Users.id = Tweets.UserId
LEFT JOIN Likes
ON Users.id = Likes.UserId
GROUP BY Users.id
ORDER BY UserTweetCount DESC;
I recommend using correlated subqueries for this:
SELECT u.*,
(SELECT COUNT(*)
FROM Tweets t
WHERE u.id = t.UserId
) AS UserTweetCount,
(SELECT COUNT(*)
FROM Likes l
WHERE u.id = l.UserId
) AS UserLikeCount
FROM Users u
ORDER BY UserTweetCount DESC;
As a note: For performance, you want indexes on Tweets(UserId) and Likes(UserId).
I'm currently outputting all of my members by adding the MySQL clause ORDER BY id DESC, but I feel that doesn't reward people that are active on my service.
I thought about judging the order by the amount of entries in another table they have under their ID.
Essentially, I'm asking if it's possible to order columns in a MAIN table counting the amount of rows where the users ID is in the column of the row.
Something pseudo to this
SELECT user_id,name,etc FROM users ORDER BY (
COUNT(SELECT FROM users_interactions WHERE user_id = user_id) *******
) ASC
In the end of the COUNT statement, the user_id = user_id was just a guess.
You are almost there - what you need to do is to put COUNT inside SELECT:
SELECT user_id,name,etc FROM users u ORDER BY (
SELECT COUNT(*)
FROM users_interactions i
WHERE i.user_id = u.user_id
) ASC
You could also do it using a JOIN, like this:
SELECT u.user_id, u.name, u.etc
FROM users u
LEFT OUTER JOIN users_interactions i ON i.user_id = u.user_id
GROUP BY u.user_id, u.name, u.etc
ORDER BY COUNT(*) ASC
This query:
SELECT
user_id,
count(base_item)
FROM items
WHERE base_item = '202'
group by user_id order by count(base_item)
Gives me this result:
which I want.
However, I also want it to exclude all user ids in the users table with a rank of 5 or greater. as shown here
Modify your where clause this way:
WHERE base_item = '202' AND user_id NOT IN (SELECT id FROM users WHERE rank > 5)
The portion in parentheses is called a subquery. The result set of the subquery contains the id of all users with a rank greater than 5. The addition to the where clause excludes all users in that result set.
Join with the users table and filter out rows with high rank
SELECT user_id, count(*) AS count
FROM items AS i
JOIN users AS u ON i.user_id = u.id
WHERE i.base_item = '202'
AND u.rank <= 5
group by user_id
order by count
I have a table posts with columns board_id, author_id, message. I have another table users with columns id, name, avatar_url.
I need to write a query to get all of the users that have posted on a given board, with no duplicates. The query should return the full user row (id, name, avatar_url).
I've tried
SELECT DISTINCT users.*, posts.author_id
FROM users
INNER JOIN posts
ON users.id = posts.author_id
WHERE posts.board_id = [desired board ID]
but that's giving me duplicates of each user.
There is also the possibility that my query is correct and I've goofed on something elsewhere...
Here's a simple query that will get you all the rows in users with post activity w/o duplication
SELECT * FROM USERS
WHERE id IN (SELECT author_id FROM posts WHERE board_id = [desired board]
You could also use your basic syntax with a distinct on everything you need distinct, e.g.:
SELECT DISTINCT users.*
FROM users
JOIN posts ON users.id = posts.author_id
WHERE posts.board_id = [desired board ID]
Just group by the user id, like so:
SELECT users.id, MIN(users.name), MIN(users.avatar_url)
FROM users
INNER JOIN posts
ON users.id = posts.author_id
WHERE posts.board_id = [desired board ID]
GROUP BY users.id
SELECT users.id, users.name, users.avatar_url, posts.author_id
FROM users
INNER JOIN posts
ON users.id = posts.author_id
WHERE posts.board_id = [desired board ID] GROUP BY users.id
This will get all found rows and then group them by the userid so each user id will appear just once, hence each user row [who posts on the board] will appear just once.
Yet better is use with annotation not for highlighted after IN, which defense against duplicate values. That's it.
I'm stuck doing a query. I'd like to extract the 10 first records of one table considering the values of the other three tables. I'll try to explain what I want with an example:
TABLES
USERS: username and date
POINTS: id_user, points
COMMENTS: id_user
WON: id_user
THE CRITERIA MUST BE: The 10 users who have more points and, in case of equal values, with more comments published, less recent date date and didn't won. In that order.
SELECT id, username, date FROM users as us LIMIT 10 ORDER BY date DESC JOIN id_user, points FROM points as po WHERE us.id = po.id_user ORDER BY po.points DESC JOIN COUNT (id_user) FROM comments JOIN COUNT (id_user) FROM won;
I know that's wrong... :(
Assuming Users has an id field and a created datetime field, I think you're looking for something like this
SELECT *
FROM Users
LEFT JOIN Points ON Points.id_user = Users.id
LEFT JOIN Comments ON Comments.id_user = Users.id
LEFT JOIN Won ON Won.id_user = Users.id
GROUP BY Users.id
ORDER BY SUM(Points.points) DESC, COUNT(Comments.id) DESC, MAX(Users.created) DESC, COUNT(Won.id) DESC