Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Column_name Type Computed Length Prec Scale Nullable
HireDate smalldatetime no 4 no
TerminationDate smalldatetime no 4 yes
ManagerEmpID int no 4 10 0 no
Department varchar no 25 no
PreviousEmployer varchar no 30 yes
DateOfBirth datetime no 8 yes
LastRaiseDate datetime no 8 no
As you can see, all of our columns have been added. The thing to note, however, is that they all went to
the end of the column list. There is no way to add a column to a specific location in SQL Server. If you
want to move a column to the middle, you need to create a completely new table (with a different name),
copy the data over to the new table, DROP the existing table, and then rename the new one.
This issue of moving columns around can get very sticky indeed. Even some of the tools that are supposed
to automate this often have problems with it. Why? Well, any foreign key constraints you have
that reference this table must first be dropped before you are allowed to delete the current version of the
table. That means that you have to drop all your foreign keys, make the changes, and then add all your
foreign keys back. It doesn’t end there, however; any indexes you have defined on the old table are automatically
dropped when you drop the existing table — that means that you must remember to re-create
your indexes as part of the build script to create your new version of the table — yuck!
But wait! There’s more! While we haven’t really looked at views yet, I feel compelled to make a reference
here to what happens to your views when you add a column. You should be aware that, even if your
view is built using a SELECT * as its base statement, your new column will not appear in your view
until you rebuild the view. Column names in views are resolved at the time the view is created for performance
reasons. That means any views that have already been created when you add your columns
have already resolved using the previous column list — you must either DROP and recreate the view or
use an ALTER VIEW statement to rebuild it.
The DROP Statement
Performing a DROP is the same as deleting whatever object(s) you reference in your DROP statement. It’s
very quick and easy, and the syntax is exactly the same for all of the major SQL Server objects (tables,
views, sprocs, triggers, and so on). It goes like this:
DROP [, ...n]
Chapter 5: Creating and Altering Tables
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