How do I add the identity property to an existing column in SQL Server

Question

In SQL Server (in my case, 2005) how can I add the identity property to an existing table column using T-SQL?

Something like:

alter table tblFoo 
            


        

Answer 1

The solution posted by Vikash doesn't work; it produces an "Incorrect syntax" error in SQL Management Studio (2005, as the OP specified). The fact that the "Compact Edition" of SQL Server supports this kind of operation is just a shortcut, because the real process is more like what Robert & JohnFX said--creating a duplicate table, populating the data, renaming the original & new tables appropriately.

If you want to keep the values that already exist in the field that needs to be an identity, you could do something like this:

CREATE TABLE tname2 (etc.)
INSERT INTO tname2 FROM tname1

DROP TABLE tname1
CREATE TABLE tname1 (with IDENTITY specified)

SET IDENTITY_INSERT tname1 ON
INSERT INTO tname1 FROM tname2
SET IDENTITY_INSERT tname1 OFF

DROP tname2

Of course, dropping and re-creating a table (tname1) that is used by live code is NOT recommended! :)