How do you add a NOT NULL Column to a large table in SQL Server?

Question

To add a NOT NULL Column to a table with many records, a DEFAULT constraint needs to be applied. This constraint causes the entire ALTER TABLE command to take a long time to

Answer 1

I had a similar problem and I went with modified #3 approach. In my case the database was in SIMPLE recovery mode and the table to which column was supposed to be added was not referenced by any FK constraints.

Instead of creating a new table with the same schema and copying contents of original table, I used SELECT…INTO syntax.

According to Microsoft (http://technet.microsoft.com/en-us/library/ms188029(v=sql.105).aspx)

The amount of logging for SELECT...INTO depends on the recovery model in effect for the database. Under the simple recovery model or bulk-logged recovery model, bulk operations are minimally logged. With minimal logging, using the SELECT… INTO statement can be more efficient than creating a table and then populating the table with an INSERT statement. For more information, see Operations That Can Be Minimally Logged.

The sequence of steps :

1.Move data from old table to new while adding new column with default

 SELECT  table.*,   cast (‘default’ as nvarchar(256)) new_column
 INTO    table_copy 
 FROM    table

2.Drop old table

 DROP TABLE  table

3.Rename newly created table

 EXEC sp_rename 'table_copy',  ‘table’

4.Create necessary constraints and indexes on the new table

In my case the table had more than 100 million rows and this approach completed faster than approach #2 and log space growth was minimal.