Question

I had an uniqueidentifier field in SQL Server (SQL Azure to be precise) that I wanted to get rid of. Initially, when I ran the code as mentioned in SQL Azure table size to determine the size of the table it was about 0.19 MB.

As a first step I set all values in the uniqueidentifier field to null. There are no constraints/indexes that use the column. Now, when I ran the code to determine the table sizes the table had increased in size to about 0.23 MB. There are no records being added to a table (its in a staging environment).

I proceeded to delete the column and it still hovered at the same range.
Why does the database size show an increase when I delete a column. Any suggestions?

Answer 1

Setting an uniqueidentifier column to NULL value does not change the record size in any way, since is a fixed size type (16 bytes). Dropping a fixed size column column does not change the record size, unless is the last column in the physical layout and the space can be reused later. ALTER TABLE … DROP COLUMN is only a logical operation, it simply marks the columns as dropped, see SQL Server Columns Under the Hood.

In order to reclaim the space you need to drop the column and then rebuild the clustered index of the table, see ALTER INDEX … REBUILD.

For the record (since SHRINK is not allowed in SQL Azure anyway) on the standalone SQL Server SHRINK would had solved nothing, this is not about page reservation but about physical record size.