I've had some questions sent in comments and I wanted to reply to some of them using a post so others who aren't subscribed to the comment sections can see the answers.
Wesley Backelant said:
I was wondering what exactly you mean by "this allows an optimization when reading columns that are NULL". Could you elaborate on that?
But with a NULL bitmap, all you have to do is:
So, its about even for a lookup of a single fixed-length column, but for variable-length columns, and for multiple row selects, there's a clear advantage to having the NULL bitmap.
Hope this makes my comment a bit clearer.
PingBack from http://www.glorf.it/blog/2006/07/03/sql-talk/sql-server-storage-engine