I have 2 tables: Persons(idPerson INT) and Questions(idQuestion INT).
I want to insert the data into a 3rd table: OrderedQuestions(idPerson INT, idQuestion INT, questionRank INT)
I want to assign all the questions to all the persons but in a random order.
I thought of doing a CROSS JOIN but then, I get the same order of questions for every persons.
INSERT INTO OrderedQuestions
SELECT idPerson, idQuestion, questionRank FROM Persons
CROSS JOIN
(SELECT idQuestion,ROW_NUMBER() OVER (ORDER BY NEWID()) as questionRank
FROM Questions) as t
How can I achieve such a random, distinct ordering for every persons?
Obviously, I want the solution to be as fast as possible.
(It can be done using TSQL or Linq to SQL)
Desired results for 3 persons and 5 questions:
idPerson idQuestion questionRank
1. 1 18 1
2. 1 14 2
3. 1 25 3
4. 1 31 4
5. 1 2 5
6. 2 2 1
7. 2 25 2
8. 2 31 3
9. 2 18 4
10. 2 14 5
11. 3 31 1
12. 3 18 2
13. 3 14 3
14. 3 25 4
15. 3 2 5
I just edited the results (Since the IDs are autogenerated, they can't be used to order the questions).
This could probably be written more efficently, but it meets all the reqs.
SELECT
idperson,
idQuestion,
ROW_NUMBER() OVER (PARTITION BY personid ORDER BY ordering) as questionRank
FROM (
SELECT idperson, idQuestion, ordering
FROM person
CROSS JOIN
(
SELECT idQuestion, NewID() as ordering FROM Question
) as t
) as a
order by personid, QuestionRank
Related
I need some help with one query.
So, I already have CTE with the next data:
ApplicationID
CandidateId
JobId
Row
1
1
1
1
2
1
2
2
3
1
3
3
4
2
1
1
5
2
2
2
6
2
5
3
7
3
2
1
8
3
6
2
9
3
3
3
I need to find one job per candidate in a way, that this job was distinct for table.
I expect that next data from query (for each candidate select the first available jobid that's not taken by the previous candidate):
ApplicationID
CandidateId
JobId
Row
1
1
1
1
5
2
2
2
8
3
6
2
I have never worked with recursive queries in CTE, having read about them, to be honest, I don't fully understand how this can be applied in my case. I ask for help in this regard.
The following query returns the expected result.
WITH CTE AS
(
SELECT TOP 1 *,ROW_NUMBER() OVER(ORDER BY ApplicationID) N,
CONVERT(varchar(max), CONCAT(',',JobId,',')) Jobs
FROM ApplicationCandidateCTE
ORDER BY ApplicationID
UNION ALL
SELECT a.*,ROW_NUMBER() OVER(ORDER BY a.ApplicationID),
CONCAT(Jobs,a.JobId,',') Jobs
FROM ApplicationCandidateCTE a JOIN CTE b
ON a.ApplicationID > b.ApplicationID AND
a.CandidateId > b.CandidateId AND
CHARINDEX(CONCAT(',',a.JobId,','), b.Jobs)=0 AND
b.N = 1
)
SELECT * FROM CTE WHERE N = 1;
However, I have the following concerns:
The recursive CTE may extract too many rows.
The concatenated JobId may exceed varchar(max).
See dbfiddle.
I have an existing table to which I have added a new column which is supposed to hold the Id of a record in another (new) table.
Simplified structure is sort of like this:
Customer table
[CustomerId] [GroupId] [LicenceId] <-- new column
Licence table <-- new table
[LicenceId] [GroupId]
The Licence table has a certain number of licences per group than can be assigned to customers in that same group. There are multiple groups, and each group has a variable number of customers and licences.
So say there are 100 licences available for group 1 and there are 50 customers in group 1, so each can get a license. There are never more customers than there are licences.
Sample
Customer
[CustomerId] [GroupId] [LicenceId]
1 1 NULL
2 1 NULL
3 1 NULL
4 1 NULL
5 2 NULL
6 2 NULL
7 2 NULL
8 3 NULL
9 3 NULL
Licence
[LicenceId] [GroupId]
1 1
2 1
3 1
4 1
5 1
6 1
7 2
8 2
9 2
10 2
11 2
12 3
13 3
14 3
15 3
16 3
17 3
Desired outcome
Customer
[CustomerId] [GroupId] [LicenceId]
1 1 1
2 1 2
3 1 3
4 1 4
5 2 7
6 2 8
7 2 9
8 3 12
9 3 13
So now I have to do this one time update to give every customer a licence and I have no idea how to go about it.
I'm not allowed to use a cursor. I can't seem to do a MERGE UPDATE, because joining the Customer to the Licence table by GroupId will result in multiple hits.
How do I assign each customer the next available LicenceId within their group in one query?
Is this even possible?
You can use window functions:
with c as (
select c.*, row_number() over (partition by groupid order by newid()) as seqnum
from customers c
),
l as (
select l.*, row_number() over (partition by groupid order by newid()) as seqnum
from licenses c
)
update c
set c.licenceid = l.licenseid
from c join
l
on c.seqnum = l.seqnum and c.groupid = l.groupid;
This assigns the licenses randomly. That is really just for fun. The most efficient method is to use:
row_number() over (partition by groupid order by (select null)) as seqnum
SQL Server often avoids an additional sort operation in this case.
But you might want to order them by something else -- for instance by the ordering of the customer ids, or by some date column, or something else.
Gordon has put it very well in his answer.
Let me break it down into simpler steps for you.
Step 1. Use the ROW_NUMBER() function to assign a SeqNum to the Customers. Use PARTITION BY GroupId so that the number starts from 1 in every group. I would ORDER BY CustomerId
Step 2. Use the ROW_NUMBER() function to assign a SeqNum to the Licences. Use PARTITION BY GroupId so that the number starts from 1 in every group. ORDER BY LicenseId because your ask is to "assign each customer the next available LicenceId within their group".
Now use these 2 queries to update LicenseId in Customer table.
It's hard to formulate, so i'll just show an example and you are welcome to edit my question and title.
Suppose, i have a table
flag id value datetime
0 b 1 343 13
1 a 1 23 12
2 b 1 21 11
3 b 1 32 10
4 c 2 43 11
5 d 2 43 10
6 d 2 32 9
7 c 2 1 8
For each id i want to squeze the table by flag columns such that all duplicate flag values that follow each other collapse to one row with sum aggregation. Desired result:
flag id value
0 b 1 343
1 a 1 23
2 b 1 53
3 c 2 75
4 d 2 32
5 c 2 1
P.S: I found functions like CONDITIONAL_CHANGE_EVENT, which seem to be able to do that, but the examples of them in docs dont work for me
Use the differnece of row number approach to assign groups based on consecutive row flags being the same. Thereafter use a running sum.
select distinct id,flag,sum(value) over(partition by id,grp) as finalvalue
from (
select t.*,row_number() over(partition by id order by datetime)-row_number() over(partition by id,flag order by datetime) as grp
from tbl t
) t
Here's an approach which uses CONDITIONAL_CHANGE_EVENT:
select
flag,
id,
sum(value) value
from (
select
conditional_change_event(flag) over (order by datetime desc) part,
flag,
id,
value
from so
) t
group by part, flag, id
order by part;
The result is different from your desired result stated in the question because of order by datetime. Adding a separate column for the row number and sorting on that gives the correct result.
I have the table below in an SQL database.
user rating
1 10
1 7
1 6
1 2
2 8
2 3
2 2
2 2
I would like to keep only the best two ratings by user to get:
user rating
1 10
1 7
2 8
2 3
What would be the SQL query to do that? I am not sure how to do it.
It will work
;with cte as
(select user,rating, row_number() over (partition by user order by rating desc) maxval
from yourtable)
select user,rating
from cte
where maxval in (1,2)
I have a table containing items in a priority order as such:
id priority
1 1
2 2
3 3
4 8
5 3
6 4
Currently I retrieve items (SQL Server) in priority order, although a random item when there are matching priorities using the following query:
select item
from table
order by priority, newid()
This will return
id priority
1 1
2 2
3 3
5 3
6 4
4 8
or
id priority
1 1
2 2
5 3
3 3
6 4
4 8
So it's approximately 50/50 traffic
I now have a requirement to only retrieve one row of the rows when there are two matching priorities, for example..
id priority
1 1
2 2
3 3
6 4
4 8
or
id priority
1 1
2 2
5 3
6 4
4 8
You can use ROW_NUMBER, presuming SQL-Server (because of NEWID):
WITH CTE AS
(
SELECT t.*, RN = ROW_NUMBER() OVER (PARTITION BY Priority
ORDER BY ID)
FROM dbo.table t
)
SELECT * FROM CTE WHERE RN = 1
If these are all columns you could also use this sql:
SELECT MIN(t.ID) AS ID, t.Priority
FROM dbo.table t
GROUP BY t.priority
Update "No, I need to be able to get a random row when two (or more) priorities match"
Then i have misunderstood your requirement. You can use ORDER BY NEWID:
WITH CTE AS
(
SELECT t.*, RN = ROW_NUMBER() OVER (PARTITION BY Priority
ORDER BY NEWID())
FROM dbo.table t
)
SELECT * FROM CTE WHERE RN = 1