INSERTING YOUR OWN IDENTITIES v7.0
When defining a table with an identity column, it is sometimes 
necessary to override the system-generated ID and replace it with your 
own or a legacy ID. There are a few rules you must follow when 
performing these tasks. Assume the following table structure and 
scenario:

CREATE TABLE TableX (IDCol INT IDENTITY(1,1) NOT NULL, 
Fname VARCHAR(10) NOT NULL, 
LName VARCHAR(10) NOT NULLl)

Normally, you can INSERT into a table that contains an ID column 
without specifying the actual ID column in the values list. For 
example:

INSERT INTO TableX VALUES ('John', 'Smith')

If you attempt to INSERT into the ID column

INSERT INTO TableX VALUES (1, 'John', 'Smith')

you should receive an error similar to "An explicit value for the 
identity column in table 'TableX' can only be specified when a column 
list is used and IDENTITY_INSERT is ON."

Use the following rules to INSERT your own identities.

1. Make use of the SET IDENTITY_INSERT <TableName> ON|OFF statement.

2. Qualify your INSERT statement with the column name(s).

3. Once completed, turn off the SET IDENTITY_INSERT <TableName> ON|OFF 
statement.

SET IDENTITY_INSERT TableX ON 
INSERT INTO TableX (IDCol, Fname, Lname) 
VALUES (1,'John', 'Smith') 
INSERT INTO TableX (IDCol, Fname, Lname) 
VALUES (2,'Mary', 'Doe') 
INSERT INTO TableX (IDCol, Fname, Lname) 
VALUES (3,'Steve', 'Martin') 
SET IDENTITY_INSERT TableX OFF

These steps provide a powerful mechanism for inserting legacy IDs as 
well as your own IDs into a table defined with an identity column.