SQL Merge duplicate rows - sql

Question

I want to change my data from this:
ID
Date
2245873
03-JAN
2245873
03-JAN
2245873
04-JAN
8394313
03-JAN
8394313
04-JAN
8394313
05-JAN
3446512
31-DEC
3446512
20-JAN
617828
31-DEC
617828
03-JAN
617828
20-JAN
61342
02-JAN
to this:
ID
date1
date2
date3
2245873
03-JAN
04-JAN
8394313
03-JAN
04-JAN
05-JAN
3446512
31-DEC
20-JAN
617828
31-DEC
03-JAN
20-JAN
61342
02-JAN
Remove the duplicate values for each ID (see ID=2245873),
List the dates associated with each ID in a row,
I don't know how many dates each ID has so the number of columns I need is unknown, is this possible?
I also need to be able to merge this new table with another, so it needs to be a view or alter table?
If there are no more dates associated with an ID I want the cell to be null
Table name: dbo.rem

Answer 1

I have taken the dynamic pivot columns formation part from the below answer
dynamic pivot query
The below logic should work
declare #tbl table(id int, date varchar(50))
insert into #tbl values(2245873,'03-Jan')
,(2245873,'03-Jan'),(2245873,'04-Jan')
,(8394313,'03-Jan'),(8394313,'05-Jan'),(8394313,'07-Jan')
select distinct * into #temp
--,ROW_NUMBER()over(order by id) rownum
from #tbl
-- This part is to generate row numbers and form the dates
select id,date,
'date' + convert(varchar,rownum) as 'datetobepivoted' into #temp1
from(
select *,ROW_NUMBER()over(partition by id order by id) rownum from #temp
)t
declare #pivotcolstbl varchar(200) = (STUFF((SELECT distinct ',isnull(' + QUOTENAME(c.datetobepivoted) + ', '''') ' + c.datetobepivoted
FROM #temp1 c
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,''))
declare #pivotcols varchar(200) = (STUFF((SELECT distinct ',' + QUOTENAME(c.datetobepivoted)
FROM #temp1 c
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,''))
declare #query varchar(max)
set #query = '
SELECT id, ' + #pivotcolstbl + ' from
(select id,date,datetobepivoted from #temp1)t
pivot(
max(date) for datetobepivoted in (' + #pivotcols + '))t1
'
exec(#query)
drop table #temp
drop table #temp1
Note: max aggregate function works on varchar too !

Answer 2

Does this work?
Trying to do a dynamic PIVOT similar to the other post linked above, but adding a field using 'Day' as a string and DENSE_RANK to determine the output columns (Date1, Date2, Date3...)
This is used both to set the #cols variable, and within the SELECT statement in brackets - where the resultant field is named [xdate].
When pivoted, it is these values that appear as column names alongside your original ID, then populated with specific dates relevent to that ID... hopefully!
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT DISTINCT ',' + QUOTENAME('Date'+ CAST(DENSE_RANK() OVER (PARTITION BY [ID] ORDER BY [date]) AS VARCHAR(MAX)) )
from sourcetable yt
group by [ID], [date]
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT [ID],' + #cols + ' from
(
select [ID], [Date], ''Date''+ CAST(DENSE_RANK() OVER (PARTITION BY [ID] ORDER BY [date]) AS VARCHAR(MAX)) as [xdate]
from sourcetable yt
) x
pivot
(
MAX([date] )
for [xdate] in (' + #cols + ')
) p '
EXECUTE(#query)
GO