I have this request :
SELECT id_user
FROM posts
GROUP BY id_user
ORDER BY COUNT(*) DESC
...which will return the id_user, ordered by their number of occurrence in the posts table.
But along with the id_user information, I would like to keep track of the COUNT(*) and store it somewhere, but I have no idea how to do it.
Use:
SELECT id_user,
COUNT(*) AS numPosts
FROM posts
GROUP BY id_user
ORDER BY COUNT(*) DESC
The column alias in the example, numPosts, can then be referenced in whatever you're already using to get the id_user column values.
you can do:
select id_user, count(*) total_count
FROM posts
GROUP BY id_user
ORDER BY COUNT(*) DESC
That way you can still retrieve the user id and the total times it appeared in the table
Related
I'm using MySQL 5.7.12. I have a simple query that looks like the following:
SELECT COUNT(id) as count, pic_id
FROM user_pictures
GROUP BY pic_id
I would like to exclude all the duplicate USER_ID records from grouping. So I did the following, however, it's not returning any result:
SELECT COUNT(id) as count, pic_id
FROM user_pictures
GROUP BY pic_id
HAVING count(user_id) = 1
What am I missing here?
Use DISTINCT so it doesn't count duplicates of the same user_id:
SELECT COUNT(id) as count, pic_id
FROM user_pictures
GROUP BY pic_id
HAVING count(DISTINCT user_id) = 1
I'm trying to fetch the most common value from a column when I group entries.
I figured I have to use a GROUP BY in order to get that working. I have the following query:
SELECT post_id, (SELECT browser from visits WHERE
id = ? GROUP BY browser ORDER BY count(browser)
DESC limit 1) as common_browser, count(id) as visits FROM `visits` group by post_id
On the "?" I want to pass the ID of the group, it does what I'm trying to do if I pass a parameter to it, i.e: id = 1.
If there's any other way to accomplish this, please let me know!
Use a correlated subquery.
SELECT post_id, (
SELECT browser
FROM visits AS v1
WHERE v1.post_id = v.post_id
GROUP by browser
ORDER BY COUNT(*) DESC
LIMIT 1) AS common_browser, COUNT(*) AS visits,
FROM visits AS v
GROUP BY post_id
I have a MySQL table "results" which has the following fields:
id (PK, AI), user_id (FK), date, score, time
I want to be able to query this table so that it sorts and returns the fields in order of score (descending order) followed by time (ascending order). So something like:
SELECT * FROM results ORDER BY score DESC, time ASC.
However, after this sorting, if more than one row has the same user_id, I only want to include the highest row.
How would I do this?
You can do this with not exists:
SELECT *
FROM results r
WHERE NOT EXISTS (select 1 from results r2 where r2.user_id = r.user_id and r2.id > r.id)
ORDER BY score DESC;
This will work best with an index on results(user_id, id).
My suggestion: SELECT user_id, max(score), time FROM results GROUP BY user_id ORDER BY score DESC;
Select id and highest score per user_id via max() and Group By. Then order the records by score descending.
EDIT: If you need the time for the user-score and there is only one entry with the same score you can use a subselect to get this time:
SELECT user_id, max(score), (
SELECT max(time)
FROM results AS r2
WHERE r2.user_id = r1.user_id
AND r2.score = max(r1.score)
) AS time
FROM results AS r1
GROUP BY user_id
ORDER BY score DESC;
I've managed to get something working at the moment.
SELECT user_id, score, time
FROM results T
WHERE T.score = (
SELECT MAX(T2.score)
FROM results T2
WHERE T2.user_id = T.user_id
)
ORDER BY score DESC, time ASC;
I would like to get all the rows from the two users with the greatest number of rows, that is, the two users with the greatest activity in a log table.
I have only found next solution: first, get the number of rows for every user, an limit it to 2:
SELECT userid, count(*) AS n_of_rows FROM my_table GROUP BY userid LIMIT 2;
Then, from the source code I'm querying the database (Python for example), query the database to get the rows of each user:
SELECT * FROM my_table where userid = $userid
Is it the best/elegant solution, taking into account SQL language itself and database performance?
Thanks!
I think what you're looking for is something like
select * from my_table where userid in
(select userid from my_table
group by userid
order by count(*) desc
limit 2)
To get the rows and keep the order, use a join with aggregation:
select t.*
from my_table t join
(select userid, count(*) as cnt
from my_table
group by userid
order by count(*) desc
limit 2
) top2
on t.userid = top2.userid
order by top2.cnt desc, userid;
Try this:
SELECT TOP 2 userid, count(*) AS n_of_rows
FROM my_table
GROUP BY userid
ORDER BY count(*) desc
I have a table tbl_user and I want to find which user_name(s) have the most repeating values in the table. I only want to retrieve those user_id(s).
I also need a separate query to find the count the of duplicate user_name(s) in the table .
First query to find the biggest amount of repeated usernames:
SELECT user_name, COUNT(user_id) AS amount
FROM tbl_user
GROUP BY user_name
ORDER BY amount DESC
And then grab id`s:
# faster way using username from last query
SELECT user_id
FROM tbl_user
WHERE user_name = '$user_name'
# longer way
SELECT user_id
FROM tbl_user
WHERE user_name = (
SELECT user_name
FROM tbl_user
GROUP BY user_name
ORDER BY COUNT(amount) DESC
LIMIT 1
)
To find the count of duplicates:
SELECT count(id) AS num_duplicates FROM tbl_users GROUP BY user_name ORDER BY num_duplicates DESC
To find the user_id's of the most duplicated user_name:
SELECT user_id FROM tbl_user
WHERE username IN ( SELECT user_id
FROM tbl_users
GROUP BY user_name
ORDER BY count(id) DESC LIMIT 0, 1)
SELECT COUNT(*) FROM tbl_user
GROUP BY tbl_user.user_name
Will give you the number of duplicate user_names. You can use a scripting language to select out the highest one if you like, or just look at the list if it's not something you need automated.
If you mean you want to count the occurences of a particular username, something like this may work for you.
select user_name,user_id,count(*) as mycount from tbl_user group by user_name order by mycount desc limit 5
This should get the top 5 entries
You could select the user_names which are duplicated with this SQL:
SELECT COUNT(1) AS duplicates, user_name
FROM tbl_user
GROUP BY user_name
HAVING duplicates > 1
Having done this, you can then use it as a subquery to find out the count of duplicate user_names
SELECT COUNT(1) AS count_of_user_names, SUM(duplicates) AS duplicate_records
FROM (
SELECT COUNT(1) AS duplicates, user_name
FROM tbl_user
GROUP BY user_name
HAVING duplicates > 1
) AS subquery
Or use it to find out the user ids:
SELECT user_id
FROM tbl_user
WHERE user_name IN (
SELECT user_name
FROM tbl_user
GROUP BY user_name
HAVING COUNT(1) > 1
)