Leaderboard toplist with current userid in center - SQL query - sql

Question

I have the following table:
+---------+------------+----------+-------+
| userId | campaignId | countryId| points|
+---------+------------+----------+-------+
| 10 | 1 | 101 | 72 |
| 3 | 1 | 101 | 30 |
| 6 | 1 | 101 | 72 |
| 4 | 1 | 101 | 49 |
| 1 | 1 | 101 | 53 |
| 8 | 1 | 101 | 67 |
| 5 | 1 | 101 | 6 |
| 7 | 1 | 101 | 87 |
| 2 | 1 | 101 | 41 |
| 11 | 1 | 101 | 76 |
| 9 | 1 | 101 | 50 |
+---------+------------+----------+-------+
I have already created a leaderboard toplist with a query like this:
select
RANK() OVER(order by T.points desc) AS rowRank,
T.UserID, T.points
from table as T
where T.campaignId=#campaignId
OFFSET (#page-1)*#limit ROWS FETCH NEXT #limit ROWS ONLY
Above query returns a regular toplist from top to bottom.
However, next requirement is to create a leaderboard toplist that returns current user Id rank + the above 2 ranked users + the 2 below ranked users, in total 5 users should be listed with current user in the center.
So additional input parameters would be:
set #userId = 8 // current user where leader board should center around
set #maxTopLimit = 2 // include 2 users ranked above current user
set #maxBottomLimit = 2 // include 2 users ranked below current user
The leaderboard returned should look like this with userId 8 in the center
+---------+------------+----------+-------+---------|
| userId | campaignId | countryId| points| rowRank |
+---------+------------+----------+-------+---------+
| 11 | 1 | 101 | 76 | 3 |
| 10 | 1 | 101 | 72 | 4 |
#####|###### 8 | 1 #########|##### 101 |### 67 |## 5 ####|########
| 9 | 1 | 101 | 50 | 6 |
| 2 | 1 | 101 | 49 | 7 |
+---------+------------+----------+-------+------+--+
How do I write a SQL query that behaves like this?

Answer 1

Move the ranking results in a subquery or common table expression.
with cte_rank as (...)
Select the target user.
from cte_rank cr where cr.UserId = #userId
Join the target row with all rows in the defined interval.
join cte_rank cr2 on cr2.RowRank >= cr.RowRank - #before and cr2.RowRank <= cr.RowRank + #after
Select all rows from the interval.
select cr2.*
Sample data
create table CampaignPoints
(
UserId int,
CampaignId int,
CountryId int,
Points int
);
insert into CampaignPoints (UserId, CampaignId, CountryId, Points) values
(10, 1, 101, 72),
( 3, 1, 101, 30),
( 6, 1, 101, 72),
( 4, 1, 101, 49),
( 1, 1, 101, 53),
( 8, 1, 101, 67),
( 5, 1, 101, 6),
( 7, 1, 101, 87),
( 2, 1, 101, 41),
(11, 1, 101, 76),
( 9, 1, 101, 50);
Solution
declare #userId int = 8;
declare #before int = 2;
declare #after int = 2;
with cte_rank as
(
select cp.UserId,
cp.CampaignId,
cp.CountryId,
cp.Points,
rank() over(order by cp.Points desc) as RowRank
from CampaignPoints cp
)
select cr2.*
from cte_rank cr
join cte_rank cr2
on cr2.RowRank >= cr.RowRank - #before
and cr2.RowRank <= cr.RowRank + #after
where cr.UserId = #userId
order by cr2.RowRank;
Result
UserId CampaignId CountryId Points RowRank
------ ---------- --------- ------ -------
10 1 101 72 3
6 1 101 72 3
8 1 101 67 5
1 1 101 53 6
9 1 101 50 7
Fiddle to see things in action.