Unable to add a “NOT NULL” column to empty table in SQL Server

Question

I understand that when adding a column to a table containing data in SQL server, the column must have a NULL option or a default. Otherwise what would SQL Server pad the new rows with?

I am at a loss as to why I can't add a NOT NULL column to an empty table however. I have tried this on two instances of SQL 2008 and one instance of SQL 2005 with no problems. However a customer with SQL 2000 does have this problem. Is this related to SQL 2000 or is it an option you can turn off. Let's hope it's an option.

Select @@Version

Microsoft SQL Server 2000 - 8.00.760 (Intel X86) Dec 17 2002 14:22:05 Copyright (c) 1988-2003 Microsoft Corporation Developer Edition on Windows NT 5.1 (Build 2600: Service Pack 3)

Select count(*) from actinv

0

ALTER TABLE [ActInv] ADD [BATCHNUMBER] NVARCHAR(50) NOT NULL

Msg 4901, Level 16, State 1, Line 1 ALTER TABLE only allows columns to be added that can contain nulls or have a DEFAULT definition specified. Column 'BATCHNUMBER' cannot be added to table 'ActInv' because it does not allow nulls and does not specify a DEFAULT definition.

Answer 1

SQL Server 2000 does not check for an empty table. What you are seeing is an improvement in SQL Server 2005/2008.

Either of the following two step processes will make the change in SQL Server 2000 against an empty table:

ALTER TABLE [ActInv] ADD [BATCHNUMBER] NVARCHAR(50) NOT NULL CONSTRAINT ActInv_Temp DEFAULT 'foo'
ALTER TABLE [ActInv] DROP CONSTRAINT ActInv_Temp

go

ALTER TABLE [ActInv] ADD [BATCHNUMBER] NVARCHAR(50) NULL 
ALTER TABLE [ActInv] ALTER COLUMN [BATCHNUMBER] NVARCHAR(50) NOT NULL 

Answer 2

I don't have access to 2000 to verify, but can you add a column with a named default, so that it succeeds, then just drop the named default?

Answer 3

The error message tells you that you cannot add the new column because it does not allow nulls and does not specify a DEFAULT definition.

You need to add a default value to the non-nullable field like this:

ALTER TABLE [ActInv] ADD [BATCHNUMBER] NVARCHAR(50) DEFAULT 'foo' NOT NULL

Edit: I just saw exactly what you do on separate SQL Server installations (2000 and 2005). If the table is truly empty perhaps the best solution is to drop/create the table. It sounds like a bug in SQL Server 2000.

Answer 4

Have you considered the following 2 in sequence:

ALTER TABLE [ActInv] ADD [BATCHNUMBER] NVARCHAR(50) 
GO

ALTER TABLE [ActInv] ALTER COLUMN [BATCHNUMBER] NVARCHAR(50) NOT NULL
GO

I think that should work on 2000 as well (I only have 2005 here)