SQL Server Query for Many to Many Relationship - how to query? - sql

Question

This is an update to my previous question : Many to many relationship
The previous solution works fine, but now I want tgo improve the results a little bit. I´d like to have all the wavelength values in one row.
So instead of the following result :
DateTimeID Wavelength SensorID
11435 1581,665 334
11435 1515,166 334
11435 1518,286 335
I'd like to have something similar to this:
DateTimeID Wavelength1 Wavelength2 SensorID
11435 1581,665 1515,166 334
11435 1518,286 335

Answer 1

You could use the following which applies a row_number() to the records:
select DateTimeID,
[1] as Wavelength1,
[2] as Wavelength2,
SensorId
from
(
select [DateTimeID], [Wavelength], [SensorID],
row_number() over(partition by DateTimeID, SensorId
order by DateTimeID) rn
from yourtable
) src
pivot
(
max(Wavelength)
for rn in ([1], [2])
) piv
See SQL Fiddle with Demo.
If you will have an unknown number of wavelength values, then you can use dynamic SQL to generate this:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME('Wavelength'+cast(rn as varchar(50)))
from
(
select row_number() over(partition by DateTimeID, SensorId
order by DateTimeID) rn
from yourtable
) src
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT DateTimeID,' + #cols + ', SensorId from
(
select [DateTimeID], [Wavelength], [SensorID],
''Wavelength''+cast(row_number() over(partition by DateTimeID, SensorId
order by DateTimeID) as varchar(50)) rn
from yourtable
) x
pivot
(
max(Wavelength)
for rn in (' + #cols + ')
) p '
execute(#query)
See SQL Fiddle with Demo