SQL Transpose rows to columns (group by key variable)? - pivot

Question

I am trying to transpose rows into columns, grouping by a unique identifier (CASE_ID).
I have a table with this structure:
CASE_ID AMOUNT TYPE
100 10 A
100 50 B
100 75 A
200 33 B
200 10 C
And I am trying to query it to produce this structure...
| CASE_ID | AMOUNT1 | TYPE1 | AMOUNT2 | TYPE2 | AMOUNT3 | TYPE3 |
|---------|---------|-------|---------|-------|---------|--------|
| 100 | 10 | A | 50 | B | 75 | A |
| 200 | 33 | B | 10 | C | (null) | (null) |
(assume much larger dataset with large number of possible values for CASE_ID, TYPE and AMOUNT)
I tried to use pivot but I don't need an aggregate function (simply trying to restructure the data). Now I'm trying to somehow use row_number but not sure how.
I'm basically trying to replicate and SPSS command called Casestovars, but need to be able to do it in SQL. thanks.

Answer 1

You can get the result by creating a sequential number with row_number() and then use an aggregate function with CASE expression:
select case_id,
max(case when seq = 1 then amount end) amount1,
max(case when seq = 1 then type end) type1,
max(case when seq = 2 then amount end) amount2,
max(case when seq = 2 then type end) type2,
max(case when seq = 3 then amount end) amount3,
max(case when seq = 3 then type end) type3
from
(
select case_id, amount, type,
row_number() over(partition by case_id
order by case_id) seq
from yourtable
) d
group by case_id;
See SQL Fiddle with Demo.
If you are using a database product that has the PIVOT function, then you can use row_number() with PIVOT, but first I would suggest that you unpivot the amount and type columns first. The basic syntax for a limited number of values in SQL Server would be:
select case_id, amount1, type1, amount2, type2, amount3, type3
from
(
select case_id, col+cast(seq as varchar(10)) as col, value
from
(
select case_id, amount, type,
row_number() over(partition by case_id
order by case_id) seq
from yourtable
) d
cross apply
(
select 'amount', cast(amount as varchar(20)) union all
select 'type', type
) c (col, value)
) src
pivot
(
max(value)
for col in (amount1, type1, amount2, type2, amount3, type3)
) piv;
See SQL Fiddle with Demo.
If you have an unknown number of values, then you can use dynamic SQL to get the result - SQL Server syntax would be:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT ',' + QUOTENAME(col+cast(seq as varchar(10)))
from
(
select row_number() over(partition by case_id
order by case_id) seq
from yourtable
) d
cross apply
(
select 'amount', 1 union all
select 'type', 2
) c (col, so)
group by col, so
order by seq, so
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT case_id,' + #cols + '
from
(
select case_id, col+cast(seq as varchar(10)) as col, value
from
(
select case_id, amount, type,
row_number() over(partition by case_id
order by case_id) seq
from yourtable
) d
cross apply
(
select ''amount'', cast(amount as varchar(20)) union all
select ''type'', type
) c (col, value)
) x
pivot
(
max(value)
for col in (' + #cols + ')
) p '
execute sp_executesql #query;
See SQL Fiddle with Demo. Each version will give the result:
| CASE_ID | AMOUNT1 | TYPE1 | AMOUNT2 | TYPE2 | AMOUNT3 | TYPE3 |
|---------|---------|-------|---------|-------|---------|--------|
| 100 | 10 | A | 50 | B | 75 | A |
| 200 | 33 | B | 10 | C | (null) | (null) |