As I was writing the series on myths around IDENTITY columns, I started to wonder whether copying a table into another using the SELECT…INTO statement copies over the IDENTITY property also.

The simplest way to answer this question was to run a simple test, which is shown below:

1. Create a table with an IDENTITY column defined, and insert some test data
   
2. Use SELECT…INTO to select data from the source table and pump it into another table
   
   
   
   • For clarity, I will be using different column names between the source and the destination columns
   
   
3. Use the catalog views – sys.columns and sys.identity_columns to confirm whether the new table was created with the IDENTITY column in place or not

USE tempdb;
GO

SET NOCOUNT ON;

--1. Prepare the environment
--   Create a table, and add some test data into it

--Safety Check
IF OBJECT_ID('tIdentity','U') IS NOT NULL
    DROP TABLE dbo.tIdentity;
GO

--Create a table
CREATE TABLE dbo.tIdentity (IdentityId INT IDENTITY(1,1),
                            IdentityValue VARCHAR(10)
                           );
GO

--Add some test data
INSERT INTO dbo.tIdentity (IdentityValue)
VALUES ('One'),
       ('Two'),
       ('Three');
GO

--2. Use SELECT..INTO to bulk insert data to a new table
SELECT SourceTable.IdentityId AS DestinationId,
       SourceTable.IdentityValue AS DestinationValue
INTO dbo.DestinationTable
FROM dbo.tIdentity AS SourceTable

--3. Check the properties of the new column - is it an IDENTITY column?
SELECT sc.name AS ColumnName,
       OBJECT_NAME(sc.object_id) AS TableName,
       sic.seed_value AS IdentitySeed,
       sic.increment_value AS IdentityIncrement,
       sic.is_nullable AS IsNullable,
       sic.last_value AS LastIdentityValueUsed
FROM sys.columns AS sc
INNER JOIN sys.identity_columns AS sic ON sc.object_id = sic.object_id
                                      AND sc.column_id = sic.column_id
WHERE ( sc.object_id = OBJECT_ID(N'dbo.DestinationTable',N'U') OR
        sc.object_id = OBJECT_ID(N'dbo.tIdentity',N'U')
      )
  AND sc.is_identity = 1;

--4. Cleanup
IF OBJECT_ID('dbo.tIdentity','U') IS NOT NULL
    DROP TABLE dbo.tIdentity;
GO

IF OBJECT_ID('dbo.DestinationTable','U') IS NOT NULL
    DROP TABLE dbo.DestinationTable;
GO

/**********************************************
               RESULTS
**********************************************/
/*
ColumnName     TableName         IdentitySeed IdentityIncrement IsNullable LastIdentityValueUsed
-------------- ----------------- ------------ ----------------- ---------- ---------------------
IdentityId     tIdentity              1              1               0             3
DestinationId  DestinationTable       1              1               0             3
*/

As can be seen from the experiment, the IDENTITY property propagates from one table to another via the SELECT…INTO clause.

Until we meet next time,

Be courteous. Drive responsibly.