SQL pivot to flatten rows into columns - sql-server

Question

I have a source table that looks like this:
+--------------+----------+------+------------+-----------+
| vehicleindex | parentid | year | make | model |
+--------------+----------+------+------------+-----------+
| 1 | 1 | 2007 | TOYOTA | SIENNA LE |
| 2 | 1 | 2005 | VOLKSWAGEN | JETTA GLS |
+--------------+----------+------+------------+-----------+
I'd like to select from this table such that the output looks like this:
+-------+--------+-----------+-------+------------+-----------+
| year1 | make1 | model1 | year2 | make2 | model2 |
+-------+--------+-----------+-------+------------+-----------+
| 2007 | TOYOTA | SIELLA LE | 2005 | VOLKSWAGEN | JETTA GLS |
+-------+--------+-----------+-------+------------+-----------+
How can I accomplish this on a SQL Server database with a pivot? There will always be either 1 or 2 vehicles in the source table. In the case where there's 1 vehicle, I would expect Year2, Make2 and Model2 to be NULL.

Answer 1

Similar to SQLZim's answer. Only difference is that the Window function Row_Number() is used just in case vehicleindex is not a consistent 1 and 2.
Select year1 = max(case when RN=1 then [year] end)
,make1 = max(case when RN=1 then make end)
,model1 = max(case when RN=1 then model end)
,year2 = max(case when RN=2 then [year] end)
,make2 = max(case when RN=2 then make end)
,model2 = max(case when RN=2 then model end)
From (
Select *
,RN = Row_Number() over (Partition By parentid Order By vehicleindex)
From YourTable
) A
Group By parentid
EDIT: Option 2 - Use PIVOT
Select *
From (
Select parentid
,item = concat(B.item,Dense_Rank() over (Partition By parentid Order By vehicleindex))
,value
From YourTable
Cross Apply ( values ('year' ,cast(Year as varchar(100)))
,('make' ,make)
,('model',model)
) B (item,value)
) A
Pivot (max(value) For [item] in ([year1],[make1],[model1],[year2],[make2],[model2]) ) p

Answer 2

Using conditional aggregation:
select
parentid
, year1 = max(case when vehicleindex=1 then [year] end)
, make1 = max(case when vehicleindex=1 then make end)
, model1 = max(case when vehicleindex=1 then model end)
, year2 = max(case when vehicleindex=2 then [year] end)
, make2 = max(case when vehicleindex=2 then make end)
, model2 = max(case when vehicleindex=2 then model end)
from t
group by parentid
returns:
+----------+-------+------------+-----------+-------+------------+-----------+
| parentid | year1 | make1 | model1 | year2 | make2 | model2 |
+----------+-------+------------+-----------+-------+------------+-----------+
| 1 | 2007 | TOYOTA | SIENNA LE | 2005 | VOLKSWAGEN | JETTA GLS |
| 2 | 2018 | TESLA | MODEL 3 | NULL | NULL | NULL |
+----------+-------+------------+-----------+-------+------------+-----------+
rextestder demo: http://rextester.com/ZTGXU25389
using this test data:
create table t (
vehicleindex int
, parentid int
, [year] int
, make varchar(32)
, model varchar(32)
);
insert into t values
(1,1,2007,'TOYOTA ','SIENNA LE')
, (2,1,2005,'VOLKSWAGEN','JETTA GLS')
, (1,2,2018,'TESLA','MODEL 3')

Answer 3

Unfortunately if you need to pivot 3 columns you need to create 3 separate pivots, then merge them in the end:
SELECT MAX(Year1) as 'Year1', MAX(Make1) as Make1, MAX(Model1) as 'Model1',
MAX(Year2) as 'Year2', MAX(Make2) as Make2, MAX(Model2) as 'Model2'
FROM
(
SELECT parentid,
[1] as 'Year1', NULL as Make1, NULL as 'model1',
[2] as 'Year2', NULL as Make2, NULL as 'model2'
FROM (
SELECT
parentid, vehicleindex, model, make , [year]
FROM #temp
) as s
PIVOT
(
max([year])
FOR vehicleindex IN ([1],[2])
) AS yearPvt
UNION
SELECT parentid,
NULL as 'Year1', [1] as Make1, NULL as 'model1',
NULL as 'Year2', [2] as Make2, NULL as 'model2'
FROM
(
SELECT
parentid, vehicleindex, model, make , [year]
FROM #temp
) as s
parentid, vehicleindex, model, make , [year]
FROM #temp
) as s
PIVOT
(
MAX([make])
FOR vehicleindex IN ([1],[2])
)AS makePvt
UNION
SELECT parentid,
NULL as 'Year1', NULL as Make1, [1] as 'model1',
NULL as 'Year2', NULL as Make2, [2] as 'model2'
FROM
(
SELECT
parentid, vehicleindex, model, make , [year]
FROM #temp
) as s
PIVOT
(
max([model])
FOR vehicleindex IN ([1],[2])
) AS modelPvt
) allPivots
Group BY parentid