How to combine multiple SQL rows into columns dynamically - sql

Question

I have a table with
+-------+-------+-----------------+
| P1_ID | P2_ID | Relationship_ID |
+-------+-------+-----------------+
| 1 | 21 | 3 |
| 1 | 32 | 3 |
| 2 | 45 | 2 |
| 2 | 65 | 1 |
| 3 | 98 | 3 |
| 3 | 94 | 4 |
+-------+-------+-----------------+
I want the final table to look like:
+-------+--------+--------+------+------+
| P1_ID | P2_ID1 | P2_ID2 | RID1 | RID2 |
+-------+--------+--------+------+------+
| 1 | 21 | 32 | 3 | 3 |
| 2 | 45 | 65 | 2 | 1 |
| 3 | 98 | 94 | 3 | 4 |
+-------+--------+--------+------+------+
I am not sure which direction to go with this. I am trying to use a pivot but I can not seem to make it work. Maybe I am doing it wrong.

Answer 1

You can use conditional aggregation for this. This isn't exactly what you stated for output because the ordering of your data is a little funky. But this should point you in the right direction.
declare #Something table
(
P1_ID int
, P2_ID int
, Realationship_ID int
)
insert #Something values
(1,21,3)
, (1,32,3)
, (2,45,2)
, (2,65,1)
, (3,98,3)
, (3,94,4)
select P1_ID
, P2_ID1 = MAX(Case when RowNum = 1 then P2_ID end)
, P2_ID2 = max(case when RowNum = 2 then P2_ID end)
, RID1 = MAX(Case when RowNum = 1 then Realationship_ID end)
, RID2 = max(case when RowNum = 2 then Realationship_ID end)
from
(
select *
, RowNum = ROW_NUMBER() over(partition by s.P1_ID order by Realationship_ID)
from #Something s
) x
group by x.P1_ID
--EDIT--
Here is a fully dynamic solution for this. I switched to using a temp table because a table variable would be out of scope for dynamic sql. Obviously in your situation you would be using a persistent table. This will order the output by P1_ID and the columns within each row by Realationship_ID.
if OBJECT_ID('tempdb..#Something') is not null
drop table #Something
create table #Something
(
P1_ID int
, P2_ID int
, Realationship_ID int
)
insert #Something values
(1,21,3)
, (1,32,3)
, (2,45,2)
, (2,65,1)
, (3,98,3)
, (3,94,4)
;
declare #DynamicPortion nvarchar(max) = '';
declare #FinalStaticPortion nvarchar(2000) = ' from OrderedResults Group by P1_ID order by P1_ID';
declare #StaticPortion nvarchar(2000) =
'with OrderedResults as
(
select *
, RowNum = ROW_NUMBER() over(partition by s.P1_ID order by Realationship_ID)
from #Something s
)
select P1_ID';
with E1(N) AS (select 1 from (values (1),(1),(1),(1),(1),(1),(1),(1),(1),(1))dt(n)),
E2(N) AS (SELECT 1 FROM E1 a cross join E1 b), --10E+2 or 100 rows
cteTally(N) AS
(
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E2
)
select #DynamicPortion = #DynamicPortion +
', MAX(Case when RowNum = ' + CAST(N as varchar(6)) + ' then P2_ID end) as P2_ID' + CAST(N as varchar(6)) + CHAR(10) +
', MAX(Case when RowNum = ' + CAST(N as varchar(6)) + ' then Realationship_ID end) as RID' + CAST(N as varchar(6)) + CHAR(10)
from cteTally t
where t.N <=
(
select top 1 Count(*)
from #Something
group by P1_ID
order by COUNT(*) desc
)
declare #SqlToExecute nvarchar(max) = #StaticPortion + #DynamicPortion + #FinalStaticPortion;
exec sp_executesql #SqlToExecute