I have 3 tables
User Table
id
Name
1
Mike
2
Sam
Score Table
id
UserId
CourseId
Score
1
1
1
5
2
1
1
10
3
1
2
5
Course Table
id
Name
1
Course 1
2
Course 2
What I'm trying to return is rows for each user to display user id and user name along with the sum of the maximum score per course for that user
In the example tables the output I'd like to see is
Result
User_Id
User_Name
Total_Score
1
Mike
15
2
Sam
0
The SQL I've tried so far is:
select TOP(3) u.Id as User_Id, u.UserName as User_Name, SUM(maxScores) as Total_Score
from Users as u,
(select MAX(s.Score) as maxScores
from Scores as s
inner join Courses as c
on s.CourseId = c.Id
group by s.UserId, c.Id
) x
group by u.Id, u.UserName
I want to use a having clause to link the Users to Scores after the group by in the sub query but I get a exception saying:
The multi-part identifier "u.Id" could not be bound
It works if I hard code a user id in the having clause I want to add but it needs to be dynamic and I'm stuck on how to do this
What would be the correct way to structure the query?
You were close, you just needed to return s.UserId from the sub-query and correctly join the sub-query to your Users table (I've joined in reverse order to you because to me its more logical to start with the base data and then join on more details as required). Taking note of the scope of aliases i.e. aliases inside your sub-query are not available in your outer query.
select u.Id as [User_Id], u.UserName as [User_Name]
, sum(maxScore) as Total_Score
from (
select s.UserId, max(s.Score) as maxScore
from Scores as s
inner join Courses as c on s.CourseId = c.Id
group by s.UserId, c.Id
) as x
inner join Users as u on u.Id = x.UserId
group by u.Id, u.UserName;
I have a table tasks that looks like this:
userId caption status id
1 Paul done 1
2 Ali notDone 18
3 Kevin notDone 12
3 Elisa notDone 13
I join it with another table users to find the number of taskswhere status = notDone. I do it like this:
SELECT u.id,
t.number_of_tasks,
FROM users u
INNER JOIN (
SELECT userId, COUNT(*) number_of_tasks
FROM tasks
WHERE status = "notDone"
GROUP BY userId
) t ON u.id = t.userId
"""
Now, I want create another column captions that somehow includes a list of all captions that were included in the countand fulfil the join + where conditions.
For example, I would expect this as one of the rows. How can I achieve this?
userId number_of_tasks captions
3 2 ["Kevin", "Elisa"]
You can use json_group_array() aggregate function inside the subquery to create the list of captions for each user:
SELECT u.id, t.number_of_tasks, t.captions
FROM users u
INNER JOIN (
SELECT userId,
COUNT(*) number_of_tasks,
json_group_array(caption) captions
FROM tasks
WHERE status = 'notDone'
GROUP BY userId
) t ON u.id = t.userId;
I'm having the following request to get all artworks inner join with their user info:
SELECT a.*, row_to_json(u.*) as users
FROM artworks a INNER JOIN users u USING(address)
WHERE (a.flag != "ILLEGAL" OR a.flag IS NULL)
ORDER BY a.date DESC
LIMIT 100
How could i have the same query but including no more than 3 entries per user?
Each user have a unique id called "address"
I think DISTINCT ON only work for 1 per user, maybe ROW_NUMBER?
Thank you in advance, i'm pretty new to DB queries.
You need an extra column in which you specify the nth time that the user is in the table. This will look something like this:
USER | N
user1 | 1
user1 | 2
user1 | 3
user2 | 1
user2 | 2
Getting the extra column in a new table can be done by using the following code
--Create new Table as T
WITH T AS (
SELECT TOP 100
a.*,
row_to_json(u.*) as users,
ROW_NUMBER() OVER(PARTITION BY u.user ORDER BY a.date DESC) AS N
FROM artworks a INNER JOIN users u USING(address)
WHERE (a.flag != "ILLEGAL" OR a.flag IS NULL) )
--Select columns from your new table
SELECT columns from T
WHERE (T.N =1 OR T.N =2 OR T.N =3)
Just an addition to your original query will do. Count the resulting records for each user and then filter by the counter value.
I am using users.address as the user id.
SELECT * from
(
SELECT a.*, row_to_json(u.*) as userinfo,
row_number() over (partition by u.address order by a.date desc) as ucount
FROM artworks a INNER JOIN users u ON a.address = u.address
WHERE a.flag != "ILLEGAL" OR a.flag IS NULL
) t
WHERE ucount <= 3
ORDER BY date DESC
LIMIT 100;
A remark - you have users as a column alias and as a table name which may cause confusion. I have changed the alias to userinfo.
Given tables, Profiles, and Memberships where a profile has many memberships, how do I query profiles based on the number of memberships?
For example I want to get the number of profiles with 2 memberships. I can get the number of profiles for each membership with:
SELECT "memberships"."profile_id", COUNT("profiles"."id") AS "membership_count"
FROM "profiles"
INNER JOIN "memberships" on "profiles"."id" = "memberships"."profile_id"
GROUP BY "memberships"."profile_id"
That returns results like
profile_id | membership_count
_____________________________
1 2
2 5
3 2
...
But how do I group and sum the counts to get the query to return results like:
n | profiles_with_n_memberships
_____________________________
1 36
2 28
3 29
...
Or even just a query for a single value of n that would return
profiles_with_2_memberships
___________________________
28
I don't have your sample data, but I just recreated the scenario here with a single table : Demo
You could LEFT JOIN the counts with generate_series() and get zeroes for missing count of n memberships. If you don't want zeros, just use the second query.
Query1
WITH c
AS (
SELECT profile_id
,count(*) ct
FROM Table1
GROUP BY profile_id
)
,m
AS (
SELECT MAX(ct) AS max_ct
FROM c
)
SELECT n
,COUNT(c.profile_id)
FROM m
CROSS JOIN generate_series(1, m.max_ct) AS i(n)
LEFT JOIN c ON c.ct = i.n
GROUP BY n
ORDER BY n;
Query2
WITH c
AS (
SELECT profile_id
,count(*) ct
FROM Table1
GROUP BY profile_id
)
SELECT ct
,COUNT(*)
FROM c
GROUP BY ct
ORDER BY ct;
I have the following query, which retrieves 4 adverts from certain categories in a random order.
At the moment, if a user has more than 1 advert, then potentially all of those ads might be retrieved - I need to limit it so that only 1 ad per user is displayed.
Is this possible to achieve in the same query?
SELECT a.advert_id, a.title, a.url, a.user_id,
FLOOR(1 + RAND() * x.m_id) 'rand_ind'
FROM adverts AS a
INNER JOIN advert_categories AS ac
ON a.advert_id = ac.advert_id,
(
SELECT MAX(t.advert_id) - 1 'm_id'
FROM adverts t
) x
WHERE ac.category_id IN
(
SELECT category_id
FROM website_categories
WHERE website_id = '8'
)
AND a.advert_type = 'text'
GROUP BY a.advert_id
ORDER BY rand_ind
LIMIT 4
Note: The solution is the last query at the bottom of this answer.
Test Schema and Data
create table adverts (
advert_id int primary key, title varchar(20), url varchar(20), user_id int, advert_type varchar(10))
;
create table advert_categories (
advert_id int, category_id int, primary key(category_id, advert_id))
;
create table website_categories (
website_id int, category_id int, primary key(website_id, category_id))
;
insert website_categories values
(8,1),(8,3),(8,5),
(1,1),(2,3),(4,5)
;
insert adverts (advert_id, title, user_id) values
(1, 'StackExchange', 1),
(2, 'StackOverflow', 1),
(3, 'SuperUser', 1),
(4, 'ServerFault', 1),
(5, 'Programming', 1),
(6, 'C#', 2),
(7, 'Java', 2),
(8, 'Python', 2),
(9, 'Perl', 2),
(10, 'Google', 3)
;
update adverts set advert_type = 'text'
;
insert advert_categories values
(1,1),(1,3),
(2,3),(2,4),
(3,1),(3,2),(3,3),(3,4),
(4,1),
(5,4),
(6,1),(6,4),
(7,2),
(8,1),
(9,3),
(10,3),(10,5)
;
Data properties
each website can belong to multiple categories
for simplicity, all adverts are of type 'text'
each advert can belong to multiple categories. If a website has multiple categories that are matched multiple times in advert_categories for the same user_id, this causes the advert_id's to show twice when using a straight join between 3 tables in the next query.
This query joins the 3 tables together (notice that ids 1, 3 and 10 each appear twice)
select *
from website_categories wc
inner join advert_categories ac on wc.category_id = ac.category_id
inner join adverts a on a.advert_id = ac.advert_id and a.advert_type = 'text'
where wc.website_id='8'
order by a.advert_id
To make each website show only once, this is the core query to show all eligible ads, each only once
select *
from adverts a
where a.advert_type = 'text'
and exists (
select *
from website_categories wc
inner join advert_categories ac on wc.category_id = ac.category_id
where wc.website_id='8'
and a.advert_id = ac.advert_id)
The next query retrieves all the advert_id's to be shown
select advert_id, user_id
from (
select
advert_id, user_id,
#r := #r + 1 r
from (select #r:=0) r
cross join
(
# core query -- vvv
select a.advert_id, a.user_id
from adverts a
where a.advert_type = 'text'
and exists (
select *
from website_categories wc
inner join advert_categories ac on wc.category_id = ac.category_id
where wc.website_id='8'
and a.advert_id = ac.advert_id)
# core query -- ^^^
order by rand()
) EligibleAdsAndUserIDs
) RowNumbered
group by user_id
order by r
limit 2
There are 3 levels to this query
aliased EligibleAdsAndUserIDs: core query, sorted randomly using order by rand()
aliased RowNumbered: row number added to core query, using MySQL side-effecting #variables
the outermost query forces mysql to collect rows as numbered randomly in the inner queries, and group by user_id causes it to retain only the first row for each user_id. limit 2 causes the query to stop as soon as two distinct user_id's have been encountered.
This is the final query which takes the advert_id's from the previous query and joins it back to table adverts to retrieve the required columns.
only once per user_id
feature user's with more ads proportionally (statistically) to the number of eligible ads they have
Note: Point (2) works because the more ads you have, the more likely you will hit the top placings in the row numbering subquery
select a.advert_id, a.title, a.url, a.user_id
from
(
select advert_id
from (
select
advert_id, user_id,
#r := #r + 1 r
from (select #r:=0) r
cross join
(
# core query -- vvv
select a.advert_id, a.user_id
from adverts a
where a.advert_type = 'text'
and exists (
select *
from website_categories wc
inner join advert_categories ac on wc.category_id = ac.category_id
where wc.website_id='8'
and a.advert_id = ac.advert_id)
# core query -- ^^^
order by rand()
) EligibleAdsAndUserIDs
) RowNumbered
group by user_id
order by r
limit 2
) Top2
inner join adverts a on a.advert_id = Top2.advert_id;
I'm thinking through something but don't have MySQL available.. can you try this query to see if it works or crashes...
SELECT
PreQuery.user_id,
(select max( tmp.someRandom ) from PreQuery tmp where tmp.User_ID = PreQuery.User_ID ) MaxRandom
from
( select adverts.user_id,
rand() someRandom
from adverts, advert_categories
where adverts.advert_id = advert_categories.advert_id ) PreQuery
If the "tmp" alias is recognized as a temp buffer of the preliminary query as defined by the OUTER FROM clause, I might have something that will work... I think the field as a select statement from a queried from WONT work, but if it does, I know I'll have something solid for you.
Ok, this one might make the head hurt a bit, but lets get the logical thing going... The inner most "Core Query" is a basis that gets all unique and randomly assigned QUALIFIED Users that have a qualifying ad base on the category chosen, and type = 'text'. Since the order is random, I don't care what the assigned sequence is, and order by that. The limit 4 will return the first 4 entries that qualify. This is regardless of one user having 1 ad vs another having 1000 ads.
Next, join to the advertisements, reversing the table / join qualifications... but by having a WHERE - IN SUB-SELECT, the sub-select will be on each unique USER ID that was qualified by the "CoreQuery" and will ONLY be done 4 times based on ITs inner limit. So even if 100 users with different advertisements, we get 4 users.
Now, the Join to the CoreQuery is the Advert Table based on the same qualifying user. Typically this would join ALL records against the core query given they are for the same user in question... This is correct... HOWEVER, the NEXT WHERE clause is what filters it down to only ONE ad for the given person.
The Sub-Select is making sure its "Advert_ID" matches the one selected in the sub-select. The sub-select is based ONLY on the current "CoreQuery.user_ID" and gets ALL the qualifying category / ads for the user (wrong... we don't want ALL ads)... So, by adding an ORDER BY RAND() will randomize only this one person's ads in the result set... then Limiting THAT by 1 will only give ONE of their qualified ads...
So, the CoreQuery restricts down to 4 users. Then for each qualified user ID, gets only 1 of the qualified ads (by its inner order by RAND() and LIMIT 1 )...
Although I don't have MySQL to try, the queries are COMPLETELY legit and hope it works for you.... man, I love brain teasers like this...
SELECT
ad1.*
from
( SELECT ad.user_id,
count(*) as UserAdCount,
RAND() as ANYRand
from
website_categories wc
inner join advert_categories ac
ON wc.category_id = ac.category_id
inner join adverts ad
ON ac.advert_id = ad.advert_id
AND ad.advert_type = 'text'
where
wc.website_id = 8
GROUP BY
1
order by
3
limit
4 ) CoreQuery,
adverts ad1
WHERE
ad1.advert_type = 'text'
AND CoreQuery.User_ID = ad1.User_ID
AND ad1.advert_id in
( select
ad2.advert_id
FROM
adverts ad2,
advert_categories ac2,
website_categories wc2
WHERE
ad2.user_id = CoreQuery.user_id
AND ad2.advert_id = ac2.advert_id
AND ac2.category_id = wc2.category_id
AND wc2.website_id = 8
ORDER BY
RAND()
LIMIT
1 )
I like to suggest that you do the random with php. This is way faster than doing it in mySQL.
"However, when the table is large (over about 10,000 rows) this method of selecting a random row becomes increasingly slow with the size of the table and can create a great load on the server. I tested this on a table I was working that contained 2,394,968 rows. It took 717 seconds (12 minutes!) to return a random row."
http://www.greggdev.com/web/articles.php?id=6
set #userid = -1;
select
a.id,
a.title,
case when #userid = a.userid then
0
else
1
end as isfirst,
(#userid := a.userid)
from
adverts a
inner join advertcategories ac on ac.advertid = a.advertid
inner join categories c on c.categoryid = ac.categoryid
where
c.website = 8
order by
a.userid,
rand()
having
isfirst = 1
limit 4
Add COUNT(a.user_id) as owned in the main select directive and add HAVING owned < 2 after Group By
http://dev.mysql.com/doc/refman/5.5/en/select.html
I think this is the way to do it, if the one user has more than one advert then we will not select it.