SQL Server : reset Id and recreate data - sql

Question

I am looking for a way to reset primary key Ids and recreate data so they are sorted by date.
Before
Pk_Col Letters_Col Date_Col
------------------------------------------
1 A 2015-02-16 00:00:00.000
2 B 2012-02-16 00:00:00.000
3 C 2014-02-16 00:00:00.000
1003 D 2009-02-16 00:00:00.000
1004 E 2008-02-16 00:00:00.000
1902 F 2016-02-16 00:00:00.000
After / desired output
Pk_Col Letters_Col Date_Col
------------------------------------------
1 E 2008-02-16 00:00:00.000
2 D 2009-02-16 00:00:00.000
3 B 2012-02-16 00:00:00.000
4 C 2014-02-16 00:00:00.000
5 A 2015-02-16 00:00:00.000
6 F 2016-02-16 00:00:00.000
I've tried so far:
DBCC CHECKIDENT ('dbo.myTable',RESEED,0);
INSERT INTO dbo.myTable (Letters_Col, Date_Col)
SELECT
Letters_Col, Date_Col
FROM
(DELETE FROM myTable OUTPUT deleted.*) d;
I have to include query below probably but I had no luck to run this query successfully with recreating data and sorting at one time:
select *
from myTable
order by cast([Date_Col] as datetime) asc

Answer 1

It can be dangerous to reset primary keys. After all, they are used for foreign key relationships, so another table might be referencing them. And, the key itself should not have any particular meaning.
However, you can do what you want using ranking functions and update:
with toupdate as (
select t.*, row_number() over (order by date) as seqnum
from myTable t
)
update toupdate
set pk_Col = seqnum;

Answer 2

If you want to update PK_Col and there isn't any foreign key:
UPDATE dbo.myTable
SET PK_Col = (SELECT COUNT(*)
FROM dbo.myTable ti
WHERE ti.DateCol <= dbo.myTable.DateCol And
ti.PK_Col <= dbo.myTable.PK_Col)