Group and expand to new columns using a SQL query? - sql

Question

Having this data:
Name
Date
John
2021-03-01 10:00
Paul
2021-03-01 11:00
Paul
2021-03-01 14:20
John
2021-03-01 15:00
Paul
2021-03-01 17:00
How can I obtain this result (Dates ordered ASC)
Name
Date1
Date2
Date2
John
2021-03-01 10:00
2021-03-01 15:00
NULL
Paul
2021-03-01 11:00
2021-03-01 14:20
2021-03-01 17:00
Thank you.

Answer 1

If you want to make your query dynamic that means no matter how many dates you have for any given name this query will generate that number of columns automatically try below query:
Schema:
create table mytable (Name varchar(50),[Date] Datetime);
insert into mytable values('John' , '2021-03-01 10:00');
insert into mytable values('Paul' , '2021-03-01 11:00');
insert into mytable values('Paul' , '2021-03-01 14:20');
insert into mytable values('John' , '2021-03-01 15:00');
insert into mytable values('Paul' , '2021-03-01 17:00');
Query:
declare #cols as varchar(max), #colsForSelect as varchar(max), #query as varchar(max);
select #colsForSelect=string_agg(concat(quotename(rn),' ', datename),',' )from(
select distinct concat('Date',rn) datename,rn from
(SELECT row_number()over(partition by name order by [date])rn from mytable)t)a
select #cols =string_agg(quotename(rn),',') from (
select distinct rn from
(SELECT row_number()over(partition by name order by [date])rn from mytable)t)a
set #query = 'Select Name, ' + #colsForSelect + ' from
(
SELECT *,row_number()over(partition by name order by [date])rn
from mytable
) x
pivot
(
max([date])
for rn in (' + #cols + ')
) p
group by Name,' + #cols
execute(#query);
Output:
Name
Date1
Date2
Date3
John
2021-03-01 10:00:00.000
2021-03-01 15:00:00.000
null
Paul
2021-03-01 11:00:00.000
2021-03-01 14:20:00.000
2021-03-01 17:00:00.000
db<>fiddle here

Answer 2

Based on Larnu's help, This worked:
WITH RNs AS(
SELECT [Name],
[DateTime],
ROW_NUMBER() OVER (PARTITION BY Name ORDER BY (SELECT NULL)) AS RN
FROM dbo.Punch
WHERE Date = '2016-04-18'
)
SELECT Name,
MAX(CASE RN WHEN 1 THEN [DateTime] END) AS Result1,
MAX(CASE RN WHEN 2 THEN [DateTime] END) AS Result2,
MAX(CASE RN WHEN 3 THEN [DateTime] END) AS Result3,
MAX(CASE RN WHEN 4 THEN [DateTime] END) AS Result4
FROM RNs R
GROUP BY Name

Answer 3

I have tried with Stuff function instead of sting_agg which was introduced in 2017 server. If you are using below 2017 version you can use the below query.
declare #column_name varchar(5000)
declare #col_name varchar(5000)
set #column_name = (select stuff((select ','+'['+cast(rn as varchar(1000))+']' from(select distinct row_number()over(partition by name order by (select null))as rn from mytable)a
for xml path('')), 1,1,''))
set #col_name = (select stuff((select ','+'['+cast(rn as varchar(1000))+']' +' Date'+cast(rn as varchar(1000)) from(select distinct row_number()over(partition by name order by (select null))as rn from mytable)a
for xml path('')), 1,1,''))
exec('select name, '+#col_name +'
from (
select row_number()over(partition by name order by (select null))rn, year([date]) yr, *
from mytable
)a
pivot
(
max([date]) for [rn] in ('+#column_name+' )
)pv')