Question

I added a new identity column, and I need to update it so that the id column goes into the identity column, then delete the old id column and rename the identity column, because you cannot change a column to an identity.

I don’t know how to do this, I guess I want to loop through each row, insert it into the same table, setting the identity field to match the id field (using IDENTITY_INSERT) but I am not familiar with loops in SQL. Any ideas?

Answer 1

You could do it with temp table something like this:

Sample table and data

create table xx
(
  OldID int
)

insert into xx values(10),(20),(30)

Add NewID as identity and get the value from OldID.

create table xxTmp
(
  OldID int,
  [NewID] int identity
)

set identity_insert xxTmp on

insert into xxTmp(OldID, [NewID])
select OldID, OldID
from xx

set identity_insert xxTmp off

drop table xx
exec sp_rename 'xxTmp', 'xx'