I'm using Enterprise Manager to alter the structure of a table that has 3 million rows. Enterprise Manager locks up whenever I try to change the nullability of one column from NOT NULL to NULL. Is this problem a known bug?

The problem might be recognized as a bug if Enterprise Manager were actually locking up. However, I suspect a different problem is causing your glitch. In T-SQL, you can use the ALTER keyword to change the nullability of a column. This operation is relatively efficient, even for large tables. However, Enterprise Manager doesn't use ALTER to change nullability.

If ...