I have a table like this:
with each row representing a review given by a user. I want to get the users by the number of distinct cities they wrote reviews in. For example:
cities, users
1,1012388
2,221758
which means that 1012388 users wrote reviews for businesses in one city only.
I tried:
select count(distinct(city)) as city, count(user_id)
from table1
group by user_id
order by count(user_id) desc
First you need to find the number of distinct city reviews that each user wrote:
SELECT user_id, COUNT(DISTINCT city) AS num_reviews
FROM table1
GROUP BY user_id
Then you can group that data by number of reviews:
SELECT num_reviews, COUNT(user_id) AS num_users
FROM (SELECT user_id, COUNT(DISTINCT city) AS num_reviews
FROM table1
GROUP BY user_id) r
GROUP BY num_reviews
ORDER BY num_users DESC
Related
I have a table posts with columns (id, user_name, thread_id).
A user can submit multiple posts for a thread. thread to post is one to many.
I need to find out who submitted max posts per thread. So the result would be
Max(Count), user_name, thread_id WHERE there will be only one row per thread_id.
The table is too huge so I wanted to get the query optimized as much as I could.
You can try with the group by and having clauses:
select t.user_name, t.thread_id , count(*) as max_count
from tbl t
group by t.user_name, t.thread_id
having count(*) = ( select count(*) as ttl
from tbl
where thread_id = t.thread_id
group by user_name
order by ttl desc
limit 1 )
select user_name, thread_id, count(*) as max
from tbl t
group by user_name, thread_id
having count(*) = (
select count(*) as cnt /* most posts per user per thread */
from tbl
group by user_name, thread_id
order by cnt desc
limit 1
)
Easy workaround for system that don't have limit is:
select user_name, thread_id, count(*) as max
from tbl t
group by user_name, thread_id
having count(*) = (
select max(cnt) from (
select count(*) as cnt /* most posts per user per thread */
from tbl
group by user_name, thread_id
) m
)
Suppose you have a table posts with fields id, user_name & thread_id.
If you want to query which user has posted the most posts on a specific thread and the total number of his posts from a table, you can achieve that with this MySQL query:
SELECT user_name, thread_id, count(thread_id)
FROM posts WHERE thread_id=1 GROUP BY user_name
ORDER BY count(thread_id) DESC LIMIT 1;
It will return only one row...
My table is
f1(drinker,shop)
The table has a list of drinkers and the shops which they visit.I need to find the most popular shop.I know I can do a simple group by of shops and order it in a descending way and limit the results to 1 but my doubt is what if two or more shop have the same number of drinkers in that case my query fails.I can't use limit 2 or 3 because I want a general working query and not a one specific to the data.I am running out of ideas.
Note:
Please don't show this way:
select shop from f1 group by shop order by count(*) desc limit 1
In that case, you have to compare the counts. Not so pretty with a group by query:
select shop
from f1
group by shop
having count(*) = (select max(cnt)
from (select count(*) as cnt
from f1
group by shop
) s
);
You could also do this as a subquery:
select shop
from f1 join
(select count(*) as cnt
from f1
group by shop
order by count(*) desc
limit 1
) f1max
group by shop
having count(*) = max(f1max.cnt);
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
)
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
I have a table called order which contains columns id, user_id, price. I would like to select each user's most expensive order - the order for which that user paid the highest price. I want to select order.user_id and order.price in the same query.
select user_id, max(price) from `order` group by user_id
SELECT order.user_id, A.price
FROM `order`
LEFT JOIN
(SELECT user_id, price FROM `order` ORDER BY price DESC) A USING (user_id)