This topic appears to be a popular one and definitely saturated in terms of the number of related posts, however, I've been working on this for 3 days and I cannot get this figured out.
I've been scouring this site and many others with potential solutions to this and some are executing, but I am not getting the expected results.
Here's what I'm trying to do...
SELECT and COUNT the number of reviews a user has submitted in the reviews table.
SELECT and COUNT the number of up-votes a user has in the reviewVotes table.
GROUP BY username (which is a key in both tables - usernames are unique, but exist in multiple rows).
Order the result set by the SUM of those COUNTs DESC. (This is something I keep trying, but can't get to even execute, so I am ordering by userReviewNum DESC right now.)
LIMIT the result set to the first 10.
The result set should give me the top 10 reviewers which is calculated by the number of reviews plus (+) the number of up-votes.
Here is my latest attempt which executes, but appears to be multiplying userReviewNum * reviewVotesNum and I need it to add them (but I have been extremely unsuccessful at any attempt to include the SUM command - so bad in fact that I am embarrassed to even show my attempts).
SELECT
reviews.username,
count(reviews.username) userReviewNum,
count(reviewVotes.username) reviewVotesNum
FROM reviews
LEFT JOIN reviewVotes ON reviews.username = reviewVotes.username
GROUP by reviews.username
ORDER BY userReviewNum DESC
LIMIT 0, 10
I've tried using a JOIN and a UNION and I can't seem to get either of them to work.
Any help anyone can provide is greatly appreciated!
UPDATE:
Here is the structure and some sample data.
Reviews Table (there are other fields, but these are the important ones):
| username | comment | rating | productID |
| foo | this is awesome! | 5 | xxxx |
| bar | i don't like this | 1 | xxxx |
| foo2 | it's ok | 3 | xxxx |
| foo | bleh - nasty | 1 | xxxx |
reviewVotes Table (again, more fields than this, but these are the important ones):
| username | voterUsername | productID |
| foo | foo2 | xxxx |
| foo2 | foo | xxxx | (the simple idea here is one user is up-voting another user's post)
So I need to count the number of reviews a user has in the Reviews table, then count the number of upvotes a user has in the reviewVotes table, and then order by the sum of those two numbers.
Additional UPDATE:
In the example above, here are the expected results:
Username | # Reviews
foo | 2
bar | 1
foo2 | 1
Username | # Up-Votes
foo | 1
foo2 | 1
Username | Total Sum
foo | 3
bar | 1
foo2 | 2
Try counting distinct reviews and votes like this:
SELECT
reviews.username,
COUNT(DISTINCT reviews.id) AS userReviewNum,
COUNT(DICTINCT reviewVotes.id) AS reviewVotesNum,
COUNT(DISTINCT reviews.id) + COUNT(DICTINCT reviewVotes.id) AS userRating
FROM
reviews
LEFT JOIN reviewVotes ON reviews.username = reviewVotes.username
GROUP by reviews.username
ORDER BY userRating DESC
LIMIT 10
Try this:
SELECT username, SUM(userReviewNum + reviewVotesNum) AS userRank
FROM (
SELECT
reviews.username,
count(reviews.username) userReviewNum,
count(reviewVotes.username) reviewVotesNum
FROM reviews
LEFT JOIN reviewVotes ON reviews.username = reviewVotes.username
GROUP by reviews.username
ORDER BY userReviewNum DESC
LIMIT 0, 10)
AS result_set
GROUP BY username
The group by there is, I think, required for the SUM to work.
Try this:
SELECT Res1.*, SUM(IF(reviewVotes.Username IS NULL, 0, 1)) AS UpVotes,
userReviewNum + SUM(IF(reviewVotes.Username IS NULL, 0, 1)) AS TotalSum FROM (
SELECT username, Count(*) AS userReviewNum
FROM reviews
GROUP BY username) AS Res1
LEFT OUTER JOIN reviewVotes ON res1.username = reviewVotes.username
GROUP BY Res1.username
ORDER BY TotalSum DESC
There result would be this:
foo 2 1 3
foo2 1 1 2
bar 1 0 1
Related
I have a problem
I have two tables
The table "Memes"
id imglink name
----------------------------------
1 img.Png Polite cat
2 img2.png Crying cat
And the table "Vote"
id idmeme vote
---------------------
1 1 5
2 1 2
3 2 4
So basically the table "meme" contains memes with their image and their name
And the table "votes" contains the notes on 5 that users assign to the memes
I would like my sql query to rank by the same the highest rated with the highest rating
I already look at other topic but the problem is that for each vote with the id of the same it duplicates in the result of the SELECT *
thank you in advance
One method is to use a subquery right in the order by:
select m.*
from memes m
order by (select max(v.vote) from vote v where v.idmeme = m.id);
Of course, you can also include this in the from clause (as an aggregation query) and use a join.
The most efficient way is to use a query that returns all the maximum votes from Vote and join it to the table:
select m.*
from Memes m left join (
select idmeme, max(vote) vote
from Vote
group by idmeme
)v on v.idmeme = m.id
order by v.vote desc, m.name
See the demo.
Results:
| id | imglink | name |
| --- | -------- | ---------- |
| 1 | img.Png | Polite cat |
| 2 | img2.png | Crying cat |
I want to show first two top voted Posts then others sorted by id
This is table
+----+-------+--------------+--------+
| Id | Name | Post | Votes |
+====+=======+==============+========+
| 1 | John | John's msg | -6 |
| 2 |Joseph |Joseph's msg | 8 |
| 3 | Ivan | Ivan's msg | 3 |
| 4 |Natalie|Natalie's msg | 10 |
+----+-------+--------------+--------+
After query result should be:
+----+-------+--------------+--------+
| Id | Name | Post | Votes |
+====+=======+==============+========+
| 4 |Natalie|Natalie's msg | 10 |
| 2 |Joseph |Joseph's msg | 8 |
-----------------------------------------------
| 1 | John | John's msg | -6 |
| 3 | Ivan | Ivan's msg | 3 |
+----+-------+--------------+--------+
I have 1 solution but i feel like there is better and faster way to do it.
I run 2 queries, one to get top 2, then second to get others:
SELECT * FROM table order by Votes desc LIMIT 2
SELECT * FROM table order by Id desc
And then in PHP i make sure that i show 1st query as it is, and on displaying 2nd query i remove entry's that are in 1st query so they don't double.
Can this be done in single query to select first two top voted, then others?
You would have to use subqueries or union - meaning you have a single outer query, which contains multiple queries inside. I would simply retrieve the IDs from the first query and add a id not in (...) criterion to the where clause of the 2nd query - thus filtering out the posts retrieved in the first query:
SELECT * FROM table WHERE Id NOT IN (...) ORDER BY Id DESC
With union the query would look like as follows:
(SELECT table.*, 1 as o FROM table order by Votes desc LIMIT 2)
UNION
(SELECT table.*, 0 FROM table
WHERE Id NOT IN (SELECT Id FROM table order by Votes desc LIMIT 2))
ORDER BY o DESC, if(o=1,Votes,Id) DESC
As you can see, it wraps 3 queries into one and has a more complicated ordering as well because in union the order of the records retrieved is not guaranteed.
Two simple queries seem to be a lot more efficient to me in this particular case.
There could be different ways to write a query that returns the rows in the order you want. My solution is this:
select
table.*
from
table left join (select id from table order by votes desc limit 2) l
on table.id = l.id
order by
case when l.id is not null then votes end desc,
tp.id
the subquery will return the first two id ordered by votes desc, the join will succeed whenever the row is one of the first two otherwise l.id will be null instead.
The order by will order by number of votes desc whenever the row is the first or the second (=l.id is not null), when l.id is null it will put the rows at the bottom and order by id instead.
I want to select N random rows from a table, but in all of these rows a specific value may only occur X times.
Table "reviews":
*--------------------*
| ID | CODE_REVIEWER |
*--------------------*
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
*--------------------*
Table "users" (I left out a lot of unimportant stuff:
*----*
| ID |
*----*
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
*----*
Example output:
For X = 3:
*-----------*
| REVIEWER |
*-----------*
| 4 |
| 1 |
| 5 |
*-----------*
For X = 2:
*-----------*
| REVIEWER |
*-----------*
| 1 |
| 5 |
| 3 |
*-----------*
For X = 1 (empty):
*-----------*
| REVIEWER |
*-----------*
So, it must be a ResultSet containing a few IDs that are different from the ID X, but these IDs may only occur in "table 2" as a "code_reviewer" N times.
So everybody can be the "reviewer" FOR 3 people, and everbody can be reviewed BY 3 people
Thanks!
Edit:
This is what I got so far:
select newid from (select id, count(*) as num from (select * from users
where id != ?) as users group by id order by RAND() LIMIT ?) as sb
where num < 3 and newid not in (select code_reviewer from reviews where id = ?)
It works perfectly, apart from that it sometimes returns for example
*---*
| 2 |
| 1 |
| 2 |
*---*
(Contains the 2 twice, which shouldn't be so)
Unfortunately, I know MSSQL and not MySQL. I will try to answer using MSSQl, and hopefully that will lead you in the right direction.
I use variables to determine how many rows I should return, and then use a simple NEWID to act as a randomizer. (It is my understanding that you would order by RAND() in MySQL instead of NEWID())
declare #userId int
select #userId = 1
declare #existingReviewCount int
select #existingReviewCount = COUNT(*) from Reviews where Id = #userId
declare #requiredRowCount int
select #requiredRowCount = 3 - #existingReviewCount
select top (#requiredRowCount) Id from Users
where #userId != Id
order by NEWID()
Now replace #userId with 1 and it will return an empty set.
This seems to be essentially a top n per group problem. There are a few ways to solve that. Here is a quick and dirty way that will give you a comma separated list of id's that you need. If you want to just explode these in your code you are good to go.
select u.*,
-- r_counts.cnt as reviews_count,
substring_index(
group_concat(u_rev.id order by rand()),
',',
greatest(3-r_counts.cnt,0)) as reviewers
from users u
join users u_rev on u.id != u_rev.id
left join (
select u.id, count(r.id) as cnt
from users u
left join reviews r on u.id = r.id
group by u.id
) r_counts on r_counts.id = u.id
left join (
select u.id, count(r.id) as cnt
from users u
left join reviews r on u.id = r.reviewer
group by u.id, r.reviewer
) as did_review_counts
on did_review_counts.id = u_rev.id
where u.id = 11
and did_review_counts.cnt < 3
group by u.id;
If you need the results another way, google "top n per group mysql" and check out some of the solutions there.
Note: the 3 above would be your review number target. Edit: Now this would need to be run only 1 at a time. Then rerun after each review was done.
feedback table
-------------------------------
|rating|feedback|feedback_date|
-------------------------------
| 5 | good | 1452638788 |
| 1 | bad | 1452638900 |
| 0 | ugly | 1452750303 |
| 3 | ok | 1453903030 |
-------------------------------
desired result
average_rating | rating | feedback | feedback_date
2.25 | 3 | ok | 1453903030
Is it possible (in a single query) to select the average of one column and also one specific row from the table?
For example, i'd like to retrieve the average of the column rating and the most recent row as a whole.
I tried the following, and also with the ORDER BY direction as DSC but they both just gave me the average_rating and the first row in the table.
SELECT AVG(f.rating) AS average_rating, f.* FROM feedback f ORDER BY feedback_date ASC
SELECT * FROM feedback NATURAL JOIN (
SELECT AVG(rating), MAX(feedback_date) feedback_date FROM feedback
) t
See it on sqlfiddle.
you can do it with a sub query like this
SELECT AVG(f.rating) AS average_rating, t1.* FROM feedback f inner join (select * from feedback order by feedback_date asc limit 1 ) t1 on true
You can put a subquery in the SELECT clause, and calculate the average in the subquery.
SELECT (SELECT AVG(rating) FROM feedback) AS avg_rating, feedback.*
FROM feedback
ORDER BY feedback_date DESC
LIMIT 1
I have the following (simplified) three tables:
user_reservations:
id | user_id |
1 | 3 |
1 | 3 |
user_kar:
id | user_id | szak_id |
1 | 3 | 1 |
2 | 3 | 2 |
szak:
id | name |
1 | A |
2 | B |
Now I would like to count the reservations of the user by the 'szak' name, but I want to have every user counted only for one szak. In this case, user_id has 2 'szak', and if I write a query something like:
SELECT sz.name, COUNT(*) FROM user_reservations r
LEFT JOIN user_kar k ON k.user_id = r.user_id
LEFT JOIN szak s ON r.szak_id = r.id
It will return two rows:
A | 2 |
B | 2 |
However I want to every reservation counted to only one szak (lets say the highest id only). I tried MAX(k.id) with HAVING, but seems uneffective.
I would like to know if there is a supported method for that in MySQL, or should I first pick all the user ID-s on the backend site first, check their maximum kar.user_id, and then count only with those, removing them from the id list, when the given szak is counted, and then build the data back together on the backend side?
Thanks for the help - I was googling around for like 2 hours, but so far, I found no solution, so maybe you could help me.
Something like this?
SELECT sz.name,
Count(*)
FROM (SELECT r.user_id,
Ifnull(Max(k.szak_id), -1) AS max_szak_id
FROM user_reservations r
LEFT OUTER JOIN user_kar k
ON k.user_id = r.user_id
GROUP BY r.user_id) t
LEFT OUTER JOIN szak sz
ON sz.id = t.max_szak_id
GROUP BY sz.name;