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

Chapter 5: Creating and Altering Tables
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Let’s say that you’ve decided you’d like to keep previous employer information on your employees
(probably so you know who will be trying to recruit the good ones back!). That just involves adding
another column, and really isn’t all that tough. The syntax looks much like it did with the CREATE
TABLE statement except that it has obvious alterations to it:
ALTER TABLE Employees
ADD
PreviousEmployer varchar(30) NULL
Not exactly rocket science — is it? Indeed, you could have added several additional columns at one time
if you had wanted to. It would look something like this:
ALTER TABLE Employees
ADD
DateOfBirth date NULL,
LastRaiseDate date NOT NULL
DEFAULT ‘2008-01-01’
Notice the DEFAULT I slid in here. We haven’t really looked at these yet (they are in our next chapter),
but I wanted to use one here to point out a special case.
If you want to add a NOT NULL column after the fact, you have the issue of what to do with rows that
already have NULL values. We have shown the solution to that here by providing a default value. The
default is then used to populate the new column for any row that is already in our table.
Before we go away from this topic for now, let’s take a look at what we’ve added:
EXEC sp_help Employees
Column_name Type Computed Length Prec Scale Nullable
EmployeeID int no 4 10 0 no
FirstName varchar no 25 no
MiddleInitial char no 1 yes
LastName varchar no 25 no
Title varchar no 25 no
SSN varchar no 11 no
Salary money no 8 19 4 no
PriorSalary money no 8 19 4 no
LastRaise money yes 8 19 4 yes