TSQL, Get top N unique rows across ordered groups - sql

Question

I have the following table of values, sorted by arbitrary segment id specified by the user. ( I know how to do that query and below are the results )
SegmentID SequenceID
3 100
3 200
3 400
3 430
1 100
1 200
1 300
1 410
2 100
2 200
2 300
2 420
I need a SQL query ( Sql Server 2012 ) that returns top N Records in order of Precedence where SequenceID is not repeated.
Example: user wants 7 sequences in order of segment preference: 3, 1,2.
The correct answer is
SegmentID SequenceID
3 100
3 200
3 400
3 430
1 300
1 410
2 420
in a nutshell, i need to traverse recordset from top to bottom, grab unique sequences as i go and add to the list.
How can I do that in a TSql statement?

Answer 1

create table #data (SegmentID int,SequenceID int);
insert into #data values
(3,100),
(3,200),
(3,400),
(3,430),
(1,100),
(1,200),
(1,300),
(1,410),
(2,100),
(2,200),
(2,300),
(2,420);
This table declares the ordering preference:
create table #prefs (Preference int, SegmentID int);
insert into #prefs values(1,3),(2,1),(3,2);
with cte as
(
select #data.SegmentID,
#data.SequenceID,
Preference,
row_number() over (partition by SequenceID order by Preference) rn
from #data
inner join #prefs on #data.SegmentID = #prefs.SegmentID
)
select SegmentId,
SequenceID
from cte
where rn = 1
order by Preference, SequenceID;

Answer 2

DEMO:
http://rextester.com/JKNKD15000
With cte (SegmentID, SequenceID) as
(SELECT 3, 100 UNION ALL
SELECT 3, 200 UNION ALL
SELECT 3, 400 UNION ALL
SELECT 3, 430 UNION ALL
SELECT 1, 100 UNION ALL
SELECT 1, 200 UNION ALL
SELECT 1, 300 UNION ALL
SELECT 1, 410 UNION ALL
SELECT 2, 100 UNION ALL
SELECT 2, 200 UNION ALL
SELECT 2, 300 UNION ALL
SELECT 2, 420),
userOrder (SegmentID, orderID) as (
SELECT 3, 1 UNION ALL
SELECT 1, 2 UNION ALL
SELECT 2, 3),
Results (SegmentID, SequenceID, RN, orderID) as (
Select A.*
, Row_number() over (Partition by A.SequenceID order by B.orderID) RN
, B.orderID
from cte A
INNER JOIN userOrder B
on A.SegmentID = B.SegmentID)
Select Top 7 *
from results where RN = 1
order by OrderID, SequenceID