How to change identity column values programmatically?

I have a MS SQL 2005 database with a table Test with column ID. ID is an identity column.

I have rows in this table and all of them have their corresponding ID auto incremented value.

Now I would like to change every ID in this table like this:

ID = ID + 1

But when I do this I get an error:

Cannot update identity column 'ID'.

I've tried this:

    ALTER TABLE Test NOCHECK CONSTRAINT ALL 
    set identity_insert ID ON

But this does not solve the problem.

I need to have identity set to this column, but I need to change values as well from time to time. So my question is how to accomplish this task.

Solution 1:

You need to

set identity_insert YourTable ON

Then delete your row and reinsert it with different identity.

Once you have done the insert don't forget to turn identity_insert off

set identity_insert YourTable OFF

Solution 2:

IDENTITY column values are immutable.

However it is possible to switch the table metadata to remove the IDENTITY property, do the update, then switch back.

Assuming the following structure

CREATE TABLE Test
(
ID INT IDENTITY(1,1) PRIMARY KEY,
X VARCHAR(10)
)

INSERT INTO Test 
OUTPUT INSERTED.*
SELECT 'Foo' UNION ALL
SELECT 'Bar' UNION ALL
SELECT 'Baz'

Then you can do

/*Define table with same structure but no IDENTITY*/
CREATE TABLE Temp
(
ID INT PRIMARY KEY,
X VARCHAR(10)
)

/*Switch table metadata to new structure*/
ALTER TABLE Test SWITCH TO Temp;

/*Do the update*/
UPDATE Temp SET ID = ID + 1;

/*Switch table metadata back*/
ALTER TABLE Temp SWITCH TO Test;

/*ID values have been updated*/
SELECT *
FROM Test

/*Safety check in case error in preceding step*/
IF NOT EXISTS(SELECT * FROM Temp)
    DROP TABLE Temp /*Drop obsolete table*/

In SQL Server 2012 it is possible to have an auto incrementing column that can also be updated more straightforwardly with SEQUENCES

CREATE SEQUENCE Seq
    AS INT
    START WITH 1
    INCREMENT BY 1

CREATE TABLE Test2
(
ID INT DEFAULT NEXT VALUE FOR Seq NOT NULL PRIMARY KEY,
X VARCHAR(10)
)

INSERT INTO Test2(X)
SELECT 'Foo' UNION ALL
SELECT 'Bar' UNION ALL
SELECT 'Baz'

UPDATE Test2 SET ID+=1

Solution 3:

Through the UI in SQL Server 2005 manager, change the column remove the autonumber (identity) property of the column (select the table by right clicking on it and choose "Design").

Then run your query:

UPDATE table SET Id = Id + 1

Then go and add the autonumber property back to the column.

Solution 4:

Firstly the setting of IDENTITY_INSERT on or off for that matter will not work for what you require (it is used for inserting new values, such as plugging gaps).

Doing the operation through the GUI just creates a temporary table, copies all the data across to a new table without an identity field, and renames the table.

Solution 5:

This can be done using a temporary table.

The idea

disable constraints (in case your id is referenced by a foreign key)
create a temp table with the new id
delete the table content
copy back data from the copied table to your original table
enable previsously disabled constraints

SQL Queries

Let's say your test table have two additional columns (column2 and column3) and that there are 2 tables having foreign keys referencing test called foreign_table1 and foreign_table2 (because real life issues are never simple).

alter table test nocheck constraint all;
alter table foreign_table1 nocheck constraint all;
alter table foreign_table2 nocheck constraint all;
set identity_insert test on;

select id + 1 as id, column2, column3 into test_copy from test v;
delete from test;
insert into test(id, column2, column3)
select id, column2, column3 from test_copy

alter table test check constraint all;
alter table foreign_table1 check constraint all;
alter table foreign_table2 check constraint all;
set identity_insert test off;
drop table test_copy;

That's it.